Pleustonic communities with Lemnaceae in South America - Landolt 1999 by JPZ.

Applied Vegetation Science 2: 7-16, 1999 © IAVS; Opulus Press Uppsala. Printed in Sweden

- PLEUSTONIC COMMUNITIES WITH LEMNACEAE IN SOUTH AMERICA -

Pleustonic communities with Lemnaceae in South America Landolt, Elias Geobotanical Institute ETHZ, Stiftung Rübel, Zürichbergstrasse 38, 8044 Zürich, Switzerland; Tel. + 41 1 632 48 46; Fax +416321215; E-mail landolt@geobot.umnw.ethz.ch

Abstract. Ca. 360 relevés of pleustonic vegetation were recorded in South America between 1983 and 1996. 245 relevés, containing three or more pleustonic species, were classified according to the methods of Braun-Blanquet. Within the class Lemnetea (minoris) the following two orders with alliances (All.) and associations (Ass.) can be distinguished: 1. Lemnetalia gibbae All. Azollo filiculoides-Lemnion gibbae Ass. Lemno minutae-Lemnetum gibbae Azollo filiculoides-Wolffielletum oblongae 2. Lemnetalia aequinoctialis All. Salvinio minimae-Lemnion minutae Ass. Lemno minutae-Wolffielletum lingulatae All. Salvinio minimae-Lemnion aequinoctialis Ass. Lemno aequinoctialis-Wolffielletum lingulatae Lemno aequinoctialis-Wolffielletum welwitschii All. Wolffio columbianae-Lemnion obscurae Ass. Wolffio globosae-Lemnetum obscurae The occurrence of the four alliances is mostly dependent on climate and geographical situation. The usefulness of creating pleustonic unities is discussed. Keywords: Duckweed; Lemna; Phytosociology; Pleustophyte; Syntaxon.

Introduction Studies of pleustonic communities from South America are rare. Eskuche (1986) reported a few Argentinian relevés. Landolt & Zarzycki (1994) partly refer to the same localities. One relevé from central Chile was described under the provisional name Lemno-Azolletum chilense by Oberdorfer (1960). It contains Azolla filiculoides, Lemna gibba and a Salvinia (under the name S. natans). Schwaar (1986) observed water vegetation from eastern Uruguay, including stands of Azolla filiculoides, Lemna gibba (under the name of L. parodiana Giardelli), Pistia stratiotes and Salvinia auriculata. From the Alto Piano in Bolivia (Lake Titicaca and Lake Uru-Uru), Libermann Cruzet al. (1988, 1991) described the Lemno minutae-Lemnetum gibbae. Landolt (1986) presented a survey of various pleustonic assemblages from South America, mostly based on herbarium studies. Within the last 15 years, the author visited South America several times and investigated Lemnaceae in

the field. Phytosociological relevés were recorded and Lemnaceae material and water samples were collected to study the relation between the occurrence of Lemnaceae and water quality. The following regions were visited (Fig. 1): - Argentina (Central and North: September to November 1983, results published in Landolt & Zarzycki 1994). - Brazil (region of Rio de Janeiro: November 1983, not considered here). - Bolivia (Central and Northeast: May 1994; July-August 1996). - Colombia (Central and North: January 1995). The present paper summarizes the phytosociological studies made during these field trips.

Methods and Study area A total of 360 stands (180 from Argentina, 100 from Bolivia, 80 from Colombia) of pleustonic assemblages with Lemnaceae were analysed according to the methods of Braun-Blanquet. All pleustonic species were noted as long as they did not form a tight cover. The relevés were grouped by hand in phytosociological tables according to the occurrence of the pleustophytes which were most frequent in the various climatic regions. The remainder of the species is arranged in order of descending frequency in these tables. 115 relevés contained only one or two pleustonic species; they were not included in the tables. The taxonomy of Salvinia is rather difficult. The author tried to identify the samples according to de la Sota (1962-1964) but was not always successful. Therefore, the identification of S. martyi and S. herzogii is not reliable. Water samples from Argentina and from the first trip to Bolivia were analysed for different parameters, according to the methods described in Landolt & Zarzycki (1994). Because of problems with custom and police controls regarding the instruments and the water bottles, the collecting and analysis of water samples was eventually discontinued. The localities of the relevés are presented in App. 1.

LANDOLT, E.

Fig. 1. Origin of the relevés in six visited regions (hatched); numbers correspond to the localities in App. 1.

Results and Discussion

Salvinio minimae-Lemnion aequinoctialis Salvinio minimae-Lemnion minutae Azollo filiculoides-Lemnion gibbae Wolffio columbianae-Lemnion obscurae

The following 10 species occur also in North America:

Lemna obscura and Wolffia globosa are reported here for South America for the first time. Both species are widespread in northern Colombia. Lemna obscura is also known from Ecuador (the species was cited as L. ecuadoriensis in Landolt 1986). Spirodela polyrrhiza, a rare species in South America, was found in Colombia, in the Provinces Cordoba (Cereté) and Huila (El Juncal). Nearly all the 29 species of pleustophytes listed in the tables are native to South America. Of these, five species are endemic to parts of South America: - Wolffiella caudata – northeastern Bolivia and possibly surrounding regions in Brazil and Peru; - Wolffia elongata – north of Venezuela and Curacao. - Salvinia martyi, S. sprucei and S. herzogii – distribution areas not known in detail. Eight species are widespread in South America and parts of Central America: Spirodela intermedia Salvinia auriculata Ceratophyllum echinatum Phyllanthus fluitans

Fig. 2. Distribution area of the four alliances.

Salvinia minima Limnobium laevigatum Ceratopteris pteridioides Eichhornia crassipes

The latter species has been introduced in tropical and subtropical areas around the world.

Azolla caroliniana Azolla filiculoides Lemna minuta Lemna obscura Lemna valdiviana Utricularia gibba Wolffia brasiliensis Wolffia columbiana Wolffiella lingulata Wolffiella oblonga The Azolla species and Lemna minuta have been introduced into Europe and other parts of the world. L. obscura might have been introduced to South America; the first collected sample from Ecuador dates from 1974.

The following seven species are distributed in more than one continent: Wolffia globosa - eastern and southern Asia from India and Indonesia north to central China and Japan; also found in Hawaii, California, Florida and Colombia, but might be introduced to these regions; Wolffiella welwitschii - in tropical regions of America and Africa; Ceratophyllum demersum Lemna gibba Pistia stratiotes Ricciocarpus natans Spirodela polyrrhiza - all distributed throughout many continents.

The following survey of the pleustonic vegetation with Lemnaceae results from the evaluation of the relevés and from herbarium studies. The relevés can be divided into three groups which are treated here as alliances: - group with Lemna gibba, L. minuta and Azolla filiculoides (Table 1); - group with L. aequinoctialis, Salvinia spec. div., and Azolla caroliniana (Tables 2 and 3); - group with L. obscura, L. aequinoctialis, Wolffia columbiana and W. globosa (Table 4). - A fourth group with Lemna minuta, Salvinia minima and Azolla caroliniana is dealt with in Landolt & Zarzycki (1994); seeTable 6.

- PLEUSTONIC COMMUNITIES WITH LEMNACEAE IN SOUTH AMERICA The distribution area of the four alliances is shown in Fig. 2. Some of the groups can be further divided on the basis of the occurrence of the Wolffiella species which they contain. Associations are only described if they form relatively stable assemblages and are documented by at least 15 relevés. Relevés with few species and a simple structure, i.e. without submerged species (Table 5), cannot be attributed to lower syntaxonomic units. Class Lemnetea (minoris) W. Koch et R. Tx. (in lit. 1954) apud R. Tx. 1955 It is reasonable to unite all pleustonic vegetation with predominant lemnids in one class on account of the structural and functional similarity. Because it is difficult to find characteristic species for the class, SchwabeBraun & Tüxen (1981) proposed to form a class group of lemnid vegetation, Wolffio-Lemnea, with Lemna and Wolffia as characteristic taxa. The author prefers to use only one order. There is at least one species occurring nearly throughout the whole distribution of the class: Ricciocarpus natans. If the introduction of foreign species from one continent to the other continues, there will be some more common species for the Lemnetea in the near future. Besides Ricciocarpus natans, the following species are found in all orders of the class, but not in all continents: Ceratophyllum demersum Lemna valdiviana Spirodela intermedia Wolffia arrhiza Wolffia columbiana.

Lemna minuta Spirodela polyrrhiza Spirodela punctata Wolffia brasiliensis

The class Lemnetea can be divided into three orders – on the basis of the results of the present study and some unpublished observations of the author: Lemnetalia minoris - cool and continental warm climate type Lemnetalia gibbae - oceanic temperate to subtropical climate type Lemnetalia aequinoctialis - subtropical to tropical climate type.

It is proposed here to separate vegetation with L. gibba, but without L. trisulca from the Lemnetalia minoris because, from a worldwide view, there would be no common species restricted to this taxon occurring throughout the order’s distribution area. From an ecological and geographical point of view, it is also reasonable to have three equivalent units characteristic of welldefined climate types. Common, but geographically and climatically restricted, species of pairs of orders are: Lemnetalia minoris and Lemnetalia gibbae: Lemna minor and Lemna turionifera; Lemnetalia minoris and Lemnetalia aequinoctialis: Lemna obscura, Lemna japonica. and Wolffia globosa; Lemnetalia gibbae and Lemnetalia aequinoctialis: Wolffiella oblonga and Limnobium laevigatum.

Order Lemnetalia minoris W. Koch et R. Tx. (in lit. 1954) apud R. Tx. 1955 Characteristic species: Lemna trisulca. Other species mainly confined to this order: Lemna disperma Lemna minor Lemna perpusilla Lemna trisulca Lemna turionifera Riccia fluitans (?) Riccia rhenana Wolffia borealis. The order is restricted to the distribution area of L. trisulca, i.e. most parts of the northern Hemisphere, eastern Africa and southern Australia. The climate is temperate to subarctic and moderately oceanic to continental. The order is not represented in South America. Order Lemnetalia gibbae nom. prov. Characteristic species: Lemna gibba. The order is distributed (similarly to the characteristic species) in southwestern North America, southern parts and the Andes of South America, in western and southern Europe, in southwestern Asia, in North, East and South Africa – stands of L. gibba with well-developed L. trisulca and abundant L. minor or L. turionifera belong to the preceding order. The climate is moderate to warm temperate, or mediterranean and rather oceanic. Waters with Lemnetalia gibbae communities are generally characterized by a high content of nitrogen, calcium and magnesium (see also Table 8). In South America, the order is represented by one alliance and at least two associations. Alliance Azollo filiculoides-Lemnion gibbae nom. prov. Typical association: Lemno minutae-Lemnetum gibbae Characteristic species : Azolla filiculoides. Other frequent species: Lemna gibba, Lemna minuta The alliance is restricted to regions of South America that are relatively cool but have mild winters. A. filiculoides and L. minuta have been introduced in Europe. Therefore, this alliance is now also represented there. The colonization of waters starts with L. gibba (waters rich in nutrients), L. minuta (less eutrophic waters) or Azolla (waters initially poor in nitrogen). L. valdiviana and Wolffiella oblonga are only present in more stable situations. In later stages, both species form a dense second layer submerged below the surface. In this situation, L. gibba may no longer form compact layers. Association: Lemno minutae-Lemnetum gibbae Libermann Cruz et al. 1988 (Table 1) The association contains the same ‘characteristic’ and ‘frequent’ species as the alliance. In addition, Lemna valdiviana is often present. It occurs in rather cool semiarid to arid regions of South America, especially in

LANDOLT, E.

3 + 2 1 + + 1 + + 1 + 3 3 3 1 1 + + 4 3 2 + + + 2 + 3 2 + 2 + 2 3 2 1 1 2 5 3 + 2 1 1 + + 1 + + 4 3 + 5 4

1 2

1 3

1 +

3 2

1 3 2 1 2 2 2 2 1 1 + 2 1 2 1 + + 2

Azolla filiculoides Lemna gibba Lemna minuta Lemna valdiviana Wolffiella oblonga Wolffiella lingulata Wolffia columbiana Wolffia brasiliensis Ricciocarpus natans Limnobium laevigatum Spirodela intermedia Ceratophyllum demersum Azolla caroliniana

In addition, the following species occur (cover-abundance values in brackets): Pistia stratiotes: Rel. 375 (2), Salvinia herzogii: 375 (2), 376 (2), Salvinia minima: 348 (+), 349 (5), 378 (2), Utricularia gibba: 261 (+), 263 (2), 266 (1).

6 6 7 8 7 5 7 3 1 4 4 2 3 4 2 1 1 + 1 2 2 + 3 2 + 2 2 3 2 1 1 4 1 2 1 3 2 2 1 1 + 1 2 2 2 2 1 1 1 2 1 5 5 2 1 5 5 2 1

4 + + +

4 3 + +

5 4 4 4 5 5 1 4 1 2 5 4 2 2 1 3 + 1 1 5

6 4 6 4 7 3 1 3 5 1 2 2 1 + 4 2 3 3 2 + + + + 4 1

7 5 1 2 1 3

8 2 2 4

8 3 1 2

8 2 + +

8 4 + 3

6 5 2 1

9 4 + 1 + 2 2 + 3 2 2

10 2 1 3

10 1 1 2

11 3 2 1 2 2 1 +

10 1 + 2 1 +

10 5 2 3

7 5 1 2

9 3 + 2 +

3 3 3 3 3 3 3 3 3 3 3 4 4 4 3 3 4 3 3 3 4 3 4 4 4 4 4 5 5 4 5 3 1 5 3 1 3 5 3 2 2 5 1 5 4 1 1 3 5 5 1 1 + 3 + 5 1 1 1 + 4 + 4 1 + 1 4 2 1 1 5 3 3 5 2 2 1 + 1 + 1 4 2 1 1 1 2 1 4 4 1 1 3 3 5 3 1 Species number

Azollo filiculoides-Wolffielletum oblongae Lemno minutae-Lemnetum gibbae

Characteristic species: Lemna aequinoctialis, Pistia stratiotes. Other pleustonic species occurring mainly in this order: Azolla caroliniana Azolla pinnata Ceratophyllum echinatum Lemna tenera Phyllanthus fluitans Salvinia species except S. natans s.l. Wolffia angusta Wolffia cylindracea Wolffia elongata Wolffia microscopica Wolffia neglecta Wolffiella species except W. oblonga. The order occurs in warm temperate to tropical climates around the world. In South America it is represented by at least four alliances and six associations.

3 3 3 3 3 3 1 1 1 1 1 1 1 1 1 0 3 3 3 3 3 2 3 3 3 3 3 3 3 3 2 2 1 3 1 2 0 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 3 3 3 3 3 2 1 5 4 5 6 6 4 5 5 5 4 5 7 5 5 6 6 5 6 5 3 3 2 2 5 6 7 5 7 6 6 3 5 3 2 3 2 2 8 2 2 2 4 4 7 7 6 8 6 6 6 7 8 7 6 9 7 4 5 3 2 9 6 0 2 8 0 4 3 0 3 9 7 8 2 8 9 0 5 1 3 6 8 6 5 0 9 6 1 1 7 4 0 1 2 2 3 2 4 7 9 8 9 5 7 9 0 2 6 3 1 1 8

Order: Lemnetalia aequinoctialis Schwabe-Braun et R.Tx. 1981 em. Landolt 1986

No. of relevĂŠ

Association Azollo filiculoides - Wolffielletum oblongae nom. prov. Typical relevĂŠ: No. 349 The association is more diverse and contains, in addition to the former association, the following species: Limnobium laevigatum Ricciocarpus natans Spirodela intermedia Wolffia brasiliensis Wolffia columbiana Wolffiella oblonga In transition zones to warmer climates, species of the Lemnetalia aequinoctialis can be found (e.g. Azolla caroliniana and Wolffiella lingulata), and stands contain up to 12 species. The association occurs in regions with milder winters and more precipitation than the Lemno minutaeLemnetum gibbae (see Table 9). It is widespread in Argentina and Chile, as well as in the tropical and subtropical Andes (2000 - 3500 m a.s.l.). The calcium, magnesium and nitrogen content of the water is lower than in the Lemno minutae-Lemnetum gibbae (Table 8). In California and Mexico, pleustonic vegetation occurs with very similar species composition (differing by the occasional presence of Lemna minor, Lemna turionifera and Spirodela polyrrhiza and by the absence of Spirodela intermedia and Limnobium laevigatum).

Table 1.

Association

southern parts of Argentina and Chile and in the Andes. In the tropical and subtropical zone it is found from 3000 - 4100 m a.s.l. Usually, the water has a high content of sodium, magnesium and calcium ions and is rich in total nitrogen (Table 8). The association avoids regions with minimum temperatures far below zero. Therefore, it does not occur in the mountains of North America with its rather continental climate. There it is replaced by associations of the Lemnetalia minoris with L. turionifera and L. trisulca.

Table 1. Azollo filiculoides-Lemnion gibbae. RelevĂŠs with cover-abundance values according to Braun-Blanquet from + to 5.

- PLEUSTONIC COMMUNITIES WITH LEMNACEAE IN SOUTH AMERICA Alliance: Salvinio minimae-Lemnion minutae nom. prov. Typical association: Lemno minutae-Wolffielletum lingulatae Characteristic species: Lemna minuta. Other frequent species: Azolla caroliniana Limnobium laevigatum Pistia stratiotes Salvinia minima Wolffiella lingulata Wolffiella oblonga The alliance is found in the floodplain of the Rio Paraná between southern Paraguay and the northern part of the province Buenos Aires. It forms a transition between the Azollo filiculoides-Wolffielletum oblongae and the Lemno aequinoctialis-Wolffielletum lingulatae. It is represented in South America by at least one association. The succession of the vegetation begins with pure stands of Lemna minuta, Azolla caroliniana or Salvinia, and ends with a floating plant cover with Scirpus cubensis – or other aquatic plant species such as Eichhornia, Limnobium and Pistia. Association: Lemno minutae-Wolffielletum lingulatae nom. prov. Typical relevé: No. 110 (cf. Landolt & Zarzycki 1994). Characteristic species: Wolffiella lingulata, Wolffiella oblonga. Other frequent species: as in the alliance. The association has the same distribution as the alliance. It is the final stage under stable water conditions before other floating species or amphibic water plants may form a tight cover. The stands have a rather complex structure with 8 - 15 pleustonic species in different layers of the water. The water is mostly poor in sodium, magnesium, calcium and nitrogen, due to a relatively high precipitation. It remains to be studied in detail if some of the relevés in Table 2 may be grouped in separate associations according to different water conditions. Alliance: Salvinio minimae-Lemnion aequinoctialis nom. prov. Typical association: Lemno aequinoctialis-Wolffielletum lingulatae (Table 2) Characteristic species: Lemna aequinoctialis. Other frequent species: Lemna valdiviana, Pistia stratiotes and Salvinia minima. The alliance is distributed throughout most of subtropical and tropical America. It is represented in South America by at least two associations. The succession of the vegetation begins with pure stands of Lemna aequinoctialis, Azolla caroliniana or Salvinia. The two mentioned associations are the end stages of the vegetation before the vegetation forms a closed and tight cover. They are separated according to the main species of the submerged layers: Wolffiella lingulata and Wolffiella welwitschii. Whether Wolffiella caudata is typical of an

association of its own, or characteristic of a regional variant of the Lemno aequinoctialis-Wolffielletum lingulatae, needs to be studied over a larger area. In this alliance, Wolffiella oblonga has a similar position as Wolffiella lingulata; it often co-occurs with the latter. Association: Lemno aequinoctialis-Wolffielletum lingulatae nom. prov. Typical relevé: No. 127 Characteristic species: Azolla caroliniana Lemna valdiviana Ricciocarpus natans Wolffiella lingulata Wolffiella oblonga. Other frequent species: Lemna aequinoctialis, Pistia stratiotes, Salvinia minima. The association is distributed throughout the area of the alliance in rather moist regions or along rivers originating from moist regions. It corresponds to the Lemno minutae-Wolffielletum lingulatae from warmer regions (especially with warmer winters). The water is characterized by low concentrations of sodium, calcium and magnesium and a relatively high nitrogen content (Table 8). Association: Lemno aequinoctialis-Wolffielletum welwitschii nom. prov. (Table 3) Typical relevé: No. 236. Characteristic species: Wolffiella welwitschii, (maybe also Ceratophyllum echinatum and Salvinia sprucei). Other frequent species: Lemna aequinoctialis, Pistia stratiotes and Salvinia minima. The association occurs in the drier regions of the area of the alliance, especially in northern Colombia. It may also be found in the Pantanál (according to indications in Pott 1993), in Venezuela, and in the northeastern part of South America. Alliance: Wolffio columbianae-Lemnion obscurae nom. prov. Typical association: Wolffio globosae-Lemnetum obscurae (Table 4) Characteristic species: Lemna obscura, Wolffia columbiana. Other frequent species: Lemna aequinoctialis Pistia stratiotes Salvinia minima Wolffia globosa. The alliance is distributed in the subtropical zone of northwestern South America, the region of Mexico and the southwestern part of the USA. In South America it is represented by at least one association. The Lemno valdivianae-Wolffielletum gladiatae Landolt 1981 from the southeast of the USA belongs to this alliance. Colonization starts mostly with Lemna obscura, followed by Lemna aequinoctialis and Wolffia species. If the conditions are stable, Wolffiella species succeed.

Lemno aequinoctialis-Wolffielletum lingulatae

No. of relevé

0 0 0 0 1 0 1 0 0 0 1 0 0 0 0 1 2 1 1 1 0 1 1 2 0 0 1 1 0 0 1 4 4 1 1 1 1 2 0 1 0 2 2 0 1 3 2 2 1 1 1 0 1 1 1 0 2 2 1 1 2 2 5 3 3 3 j 3 2 1 2 3 3 0 2 4 1 1 0 9 2 4 9 5 1 1 0 4 9 7 7 1 3 5 2 8 2 4 2 7 6 0 3 0 3 2 4 3 0 9 0 8 1 1 3 0 8

Species number

11 12 11 11 10 9 6 8 12 5 3 8 12 10 10 9 8 9 8 8 9 9 7 7 8 11 8 8 6 6 6 10 10 4 6 5 4 8 7

7 4 6 4 4 3 5 5 3 7 6 6 8 5 7 4 9 5 4 7 4 4 9 6

Lemna aequinoctialis Wolffiella lingulata Azolla caroliniana Lemna valdiviana Salvinia minima Pistia stratiotes Wolffiella oblonga Ricciocarpus natans Salvinia martyi Wolffia columbiana Wolffia brasiliensis Spirodela intermedia Utricularia gibba Limnobium laevigatum Wolffiella caudata Phyllanthus fluitans Wolffiella welwitschii Salvinia sprucei Ceratophyllum echinatum Ceratopteris pteridioides Eichhornia crassipes

1 1 + 3 2 + +

2 2 3 1 + 1 2 5 3 + 1 2 1 3 4 1 + + 1 + 2 + 1 2 1 2 5 + 1 1 2 1 + 2 + 2 + +

1 2 + 4 1

1 2 + 1

+ 1 + 1 4 + 1 1 1 2 + 1 1 + 1 + + + + + 1 + 1

2 1 + 1 1 1

+ + + 2 3

5 1 2 3

3 1 + 3 + + 3 2 1 4 1 1 1 1 2 2 1 1 3 + 1 + 1 1 + + 1 1

1 1 + 1 1 + 1 + 1

+ 1 + 1 2 + 1 1 2

+ + + 2 4 + + 1 1

1 2 1 1 4 + 1 1

1 1 2 + 2 1 1

+ 1 + 3 1 4

1 2 + 1 4 1

2 + + + + +

+ 2 1 1 + 2

1 1 + 2 2

+ 3 3 3 2

2 2 3 2 3

1 2 + 2 1

+ 1 4 3 3 2

+ 1 2 1 3 1 3 3 1

2 2 + 3 + + 1 + 3 1 1 2 3 3 + 1 2 1 + +

2 2

+ 1

+ 1 2 +

4 1 3 3

3 1 3 2

3 2 3 2

1 1 1 3

+ 2 3 3 2 1 1 2 3 1 + 4 4 5 3 2 + 3 3 2 1 1 1 1 2 1 2 3 1 3 3 1 2 4 4 2 2 2 2 2 1 + 1 1 3 + +

1 1 2 0 0 2 2 4 1 1 1 1 1 1 0 1 3 1 1 0 1 1 0 2 2 4 5 2 2 7 4 2 1 4 3 3 3 4 3 3 9 4 3 1 4 2 3 5 4 4 1 8 6 7 1 7 6 2 0 6 9 5 5 4 9 0 5 9 6 5 2 7

3 1 1 1 2 + 2 2 2 1 4 1 1 1 1 + 2 1 2 3

1 + 1

+ 1 2 2 +

3 2 3

Association

Table 2.

Table 2. Salvinio minimae-Lemnion aequinoctialis I. Relevés with cover-abundance values according to Braun-Blanquet from + to 5.

1 4 4 3 5 + 3 + 3 1 4 3 3 3 2 2 2 2 3 5 4 2 1 1 + 2 5 3 1 2 3 2 2 3 5 2 2

+ 5 + 2 1 + 3 1 2 2 1 2 2 1 2 + 4 2 4 + + 4 5 1 5 2 + + + 1 1 2 1 4 4 4 5 1 2 2 1 2 1 + 3

3 3 2 1

2 1 +

1 +

2 1 5

2 4

Table 3.

Table 3. Salvinio minimae-Lemnion aequinoctialis II. Association

Lemno aequinoctialis-Wolffielletum welwitschii

No. of relevé

253 245 225 237 236 256 255 234 232 254 258 249 213

Species number

Lemna aequinoctialis Wolffiella welwitschii Pistia stratiotes Salvinia minima Wolffiella lingulata Salvinia martyi Wolffia columbiana Azolla caroliniana Ceratopteris pteridioides Utricularia gibba Salvinia sprucei Ceratophyllum echinatum Wolffiella oblonga Lemna valdiviana Limnobium laevigatum Spirodela intermedia

1 2 + 1 2 2 1 1 1

2 2 + 4 2 1 1 1

2 2 1 + 3 1 1 1

+ 1 1 4 2 1 1

1 2 1 1 2 1

+ 3 1 1 2

1 2 2 2 2

+ 1 2 2 2 1

1 4 + 4

1 2 + 1 2

+ 1 + 1

1 3

3 1 2

+ 1 5

4 2 +

+ + +

3 2 +

2 2 5

3 2 1

1 2 2

2 2

3 2

3 + 1

1 2

4 +

+ 1

1 1 1

+ 1 1 1

2 2 1 1

3 3 1

1 1

+ 4

In addition, the following species occur (cover-abundance values in brackets): Wolffia brasiliensis Rel. 105 (5), Eichhornia crassipes 255 (1).

2 3

1 2

1 2 1 1

2 2

3 +

1 1

2 2 +

244 259 105 221 215 235 260 217 243 216 220

LANDOLT, E.

In addition, the following species occurs (cover-abundance value in brackets): Spirodela polyrrhiza: Rel. 241 (4).

- PLEUSTONIC COMMUNITIES WITH LEMNACEAE IN SOUTH AMERICA Association: Wolffio globosae-Lemnetum obscurae nom. prov. Typical relevé: No. 206. Characteristic species: Wolffia globosa Other frequent species: Lemna obscura, Lemna aequinoctialis , Wolffia columbiana, Pistia stratiotes. The association is distributed within coastal regions of northern Colombia. It may also occur in western Ecuador and northern Venezuela.

azurea. Their effect on lemnid plants is restricted to the fixation in the water and to shading. On the other side, small single plants of Eichhornia and especially Limnobium and Pistia are mostly integrated in the Lemnetea vegetation. In the tables these three species are always recorded, even if they dominate. It is difficult to draw a limit of size up to which plants belong to Lemnetea vegetation. Assemblages with dominant Utricularia and Ceratophyllum Water vegetation dominated by Utricularia (mostly U. gibba) is characteristic of waters poor in nutrients especially K, Ca, and Mg (Landolt & Zarzycki 1994). Such assemblages belong to separate phytosociological classes (Utricularietea, Potamogetonetea). If Utricularia occurs with low frequency compared to the frequency of small Lemnetea species, the vegetation should be included in the Lemnetea. Assemblages with Ceratophyllum demersum are typical of a high nutrient content. They are frequently associated with Lemnaceae and are then treated as Lemnetea species. On the other hand they often can be connected with Potamogetonetea vegetation.

Additional assemblages Beside the phytosociological taxa enumerated here, the following pleustonic assemblages can be observed in South America which probably do not belong to the Lemnetea, or grow outside of the investigated area: Assemblages with dominant water ferns (Azolla, Salvinia) Dominant occurrence of Salvinia and Azolla indicates mostly waters too low in nitrogen or/and phosphorus for the growth of Lemnaceae and marks in this way just a pioneer stage of Lemnetea taxa. However, Salvinia can, in the end, form a closed cover which proceeds into floating mats with Cyperaceae and other water plants, whereby stages with Lemnaceae are omitted. It is possible that some stable associations with Salvinia (without the permanent presence of Lemnaceae) can be recognized. This needs to be studied in detail.

Lemnetea vegetation in South America outside the study area From herbarium studies it can be concluded that in the eastern part of South America, different Lemnaceae occur which form, at least partly, different vegetation. Between Sao Paulo and Rio de Janeiro Spirodela punctata is widespread (probably introduced). From Rio northwards to the Guayanas Wolffiella neotropica is endemic. A few relevés of the author around Rio show stands with these and other species which seem to form a separate association within the Salvinio minimae- Lemnion aequinoctialis. Other associations might occur in the lower Amazonian region which is not well represented in herbaria.

Assemblages with dominant Pistia, Limnobium and Eichhornia Many waters in South America are covered either by a closed mat of Pistia stratiotes, Limnobium laevigatum or Eichhornia crassipes. These plants are much taller than the Lemnaceae and form independent communities. However, these can co-occur with Lemnetea vegetation like stands of reed or other rooted water plants covering the water surface, e.g. Ludwigia repens or Eichhornia

Table 4. Wolffio columbianae-Lemnion obscurae. Relevés with cover-abundance values according to Braun-Blanquet from + to 5. In addition, the following species occur (cover-abundance values in brackets): Ceratophyllum echinatum: Rel. 252 (2), Ceratopteris pteridioides: (231), Eichhornia crassipes: 229 (1), Lemna valdiviana: 231 (3), Limnobium laevigatum: 231 (1), Salvinia sprucei: 205 (2). Association No. of relevé

Wolffio globosae-Lemnetum obscurae 223

205

231

233

224

206

229

228

214

252

227

222

204

208

209

Species number

Lemna obscura Wolffia columbiana Lemna aequinoctialis Wolffia globosa Wolffiella lingulata Wolffiella welwitschii Wolffiella oblonga Wolffia elongata Pistia stratiotes Azolla caroliniana Salvinia minima Utricularia gibba Salvinia martyi Wolffia brasiliensis Spirodela intermedia

+ 1 2 + 2

2 1 1 2 1

+ 3 2 1 2

+ 4 2 1

+ 4 4 1

5 5 + 2

3 4 2 2

1 1 + 2

1 2 2

5 4 +

+ 4 3

5 4

1 1 2

1 1 3

3 4 1 1 2

1 1

2 1 1 +

1 2 2

2 3 5

1 2

1 1

212

2 3 2 5

LANDOLT, E.

Table 5. Pleustonic assemblages within the order Lemnetalia aequinoctialis which cannot be classified into lower-rank units. No. of relevé

423

432

141

130

449

118

327

274

120

488

431

304

239

238

247

275

112

146

Species number

Lemna aequinoctialis Azolla caroliniana Pistia stratiotes Wolffia columbiana Lemna valdiviana Ricciocarpus natans Spirodela intermedia Wolffia brasiliensis Utricularia gibba Salvinia minima Spirodela polyrrhiza Limnobium laevigatum Ceratophyllum echinatum

2 4 3

4 4 2

+ 1 +

4 3

4 1

1 1

3 3

5 1

+ 1

4 3

3 2

4 1

1 2 2

3 3

1 1

1 5

+ +

5 2

2 1

2 2

+ 2 1

2 1

2 3

I recorded Wolffia elongata only twice in Colombia, in the Wolffio globosae-Lemnetum obscurae. However, the species might have its main distribution in an unknown seasonal pleustonic formation – I visited Colombia during the dry season. In culture, the species is readily flowering which is typical of annual species. An exact climatic characterization of the habitat of the various pleustonic communities is not possible because climate stations are very rare in South America. The values given in Table 9 are, therefore, only preliminary. From the climatic factors, mean, minimum and maximum temperatures are important for the growth and survival of Lemnaceae. In addition, the factor of Martonne gives a valuable indication of the water quality. This factor is the coefficient of the precipitation in cm divided by the temperature in °C + 10. It can be

Table 6. Comparison of species frequencies in (1) Azollo filiculoides-Lemnion gibbae; (2) Salvinio minimae-Lemnion minutae; (3) Salvinio minimae-Lemnion aequinoctialis, (4) Wolffio columbianae-Lemnion obscurae. I to V: frequency classes according to Braun-Blanquet. Alliance

Azolla filiculoides Lemna gibba Lemna minuta Ceratophyllum demersum Salvinia herzogii Ricciocarpus natans Wolffia brasiliensis Lemna valdiviana Wolffiella oblonga Spirodela intermedia Limnobium laevigatum Wolffiella lingulata Azolla caroliniana Salvinia minima Utricularia gibba Pistia stratiotes Lemna aequinoctialis Wolffia columbiana Salvinia martyi Wolffiella welwitschii Salvinia sprucei Ceratophyllum echinatum Ceratopteris pteridioides Wolffiella caudata Phyllanthus fluitans Lemna obscura Wolffia globosa Wolffia elongata

V V IV I I II II III III I II I I I I I

I I V I II III II II III III IV V V IV I IV I III

III

II II III III II II IV IV III II III V II II II I I I I I

I I I I I I II II I III V V I I I I I

V IV I

assumed that the higher the value, the lower the nutrient concentration of the water (especially calcium, potassium, sodium and magnesium ions). It is difficult to characterize water quality factors in a reliable way and conclusive for the occurrence of pleustonic communities. Therefore, the water-chemical results (Table 8) only give a general impression of the nutrient situation. For pleustonic vegetation, seasonal variation is important, which we have not measured. Also the whole stock of nutrients in the ecosystem outside of the water (biomass, soil) should be known. For example, the phosphorus concentration varies considerably within the same association and during the year. The results of Table 8 show a clear variation between the associations regarding the contents of calcium, magnesium and sodium ions and of total nitrogen. The climate (Table 9) does not only directly effect the growth of the pleustophytes but also influences the nutrient content and temperature of the water. Wolek (1997) concluded from his studies of the cooccurrence of pleustonic species in Poland that the floristic composition of a given pleustonic assemblage is determined by a combination of abiotic factors and random events, and that species interactions, even if Table 7. Comparison of species frequencies of the two Salvinio minimae-Lemnion aequinoctialis associations, A: Lemno aequinoctialis-Wolffielletum lingulatae; B: Lemno aequinoctialis-Wolffielletum welwitschii. Species rare in both associations have been omitted. I to V: as in Table 6. Association

Ricciocarpus natans Lemna valdiviana Wolffiella lingulata Wolffiella oblonga Azolla caroliniana Spirodela intermedia Wolffia brasiliensis Lemna aequinoctialis Salvinia minima Utricularia gibba Ceratopteris pteridioides Salvinia martyi Wolffia colombiana Pistia stratiotes Wolffiella welwitschii

III IV V III IV II II V III II I II II III

B I III I I I I V III II II III III IV V

- PLEUSTONIC COMMUNITIES WITH LEMNACEAE IN SOUTH AMERICA Table 8. Mean values and standard error of some water parameters of four pleustonic associations in South America; 1 = Lemno minutae-Lemnetum gibbae; 2 = Azollo filiculoidesWolffielletum oblongae; 3 = Lemno minutae-Wolffielletum lingulatae; 4 = Lemno aequinoctialis-Wolffielletum lingulatae. Association n C Na Mg Ca Ntot

1 15 847/ 75 178/29 27/ 3 38/ 6 1.52/0.27

34 1040 / 333 174/52 19/9 16/5 0.54/0.17

58 188/18 60/39 2.4/0.3 4.3/0.8 0.60/0.15

4 28 66/25 3.2/0.4 1.7/0.2 6.3/1.6 1.70/0.23

n = number of samples; C = conductivity in µS/cm; Na = sodium in mg/l; Mg = magnesium in mg/l; Ca = calcium in mg/l; Ntot = total nitrogen in mg/l.

they would exist, do not contribute to any community structure. Thus assemblages of pleustonic species are only random subsets of a given species pool. This would support the view that any syntaxonomic scheme for pleustonic plant communities based on floristic criteria must fail. Wolek postulated that it is more reasonable to define an ecological group of pleustonic species characteristic of a particular habitat type by means of a combination of water body and vegetation types. The question arises whether it is reasonable to classify our relevés into the Braun-Blanquet syntaxonomic system. The main advantage of this system is that it enables us to interpret habitat conditions from the floristic analysis in a simple way, assuming that we are able to identify the species and that we know their ecological requirements and tolerances. Of course, the Braun-Blanquet approach does not give us a deeper insight in the community structure. Another aspect is that phytosociological units might be either discrete – where the spatial pattern of environmental factors is discontinuous – or, more often, show transitions to related units. I agree with Wolek that the composition of initial pleustonic assemblages in newly created waters is unpredictable and dependent on the species which are available for colonization. The first species to arrive are those which float on the water surface. The better the species is adapted to the local climate, the faster it can multiply, the more successful it will be in colonizing the new habitat. In every climate of the world at least one initial pleustonic species, called main species here, is prevalent. And it are these main species which are suited as characteristic species for Braun-Blanquet units, at least of higher hierarchical levels. The present study reveals: - Lemna aequinoctialis: subtropical and tropical climate type; - Lemna obscura: semi-arid subtropical climate type; - Lemna gibba: mediterranean climate type.

Table 9. Approximate range of climatic factors of the habitat of pleustonic assosiations in South America. Association

Mart.

Lemno minutae-Lemnetum gibbae 1.5 - 3.5 Azollo filiculoides-Wolffielletum oblongae 2.5-4.0 Lemno minutae-Wolffielletum lingulatae 3.5-4.5 Lemno aequinoctialis-Wolffielletum lingulatae 4.0-8.0 Lemno aequinoctialis-Wolffielletum welwitschii 3.0-4.5 Wolffio globosae-Lemnetum obscurae 2.5-4.0

Mean 5 - 12 10-18 15-23 20-28 20-30 15-25

Min Max 0 5 10 15 15 10

22 24 26 30 30 28

Mart. = factor of Martonne (mean annual precipitation in cm divided by the mean annual temperature in °C + 10); Mean = mean annual temperature in °C; Min = mean temperature in °C of the three coolest months; Max = mean temperature in °C of the three warmest months.

Other species may be first colonizers; they are dispersed mostly by birds. Factors such as nutrient conditions, water movements, or periodical drying out, can prevent further succession. Under such circumstances, pleustonic assemblages consist of only 1 - 4 species. It is then difficult to decide whether this reflects special local conditions or a random assemblage in an initial stage of succession. Therefore, a syntaxonomic classification cannot be recommended if only few species are present. If succession proceeds and the pleustonic vegetation develops into a more diverse, rather complex free-floating community with 3 - 15 species arranged in several layers, classification is quite possible. Smaller climatic and/or geographic differences manifest themselves in the presence or absence of additional species, of which especially the submerged species are useful for the differentiation into associations. In these later stages, competition for light and nutrients exists, and the community structure does not differ from many terrestrial communities. In general, most nutrients remain in the biomass or within the soil of the bottom. They are released from the soil and can be taken up first by species suspended near the bottom. Therefore, submerged species in the later stages of succession are more frequent than those floating on the surface. In waters with sufficient nutrient supply, the surface species form a cover, preventing the lower layers of plants from getting enough light. Sometimes, the succession proceeds into a tight floating plant cover of various aquatic and amphibic plants. Some pleustophytes may survive in these mats. In addition, Wolffiella species and Lemna valdiviana often grow heterotrophically below this mat. It is obvious that each assemblage of pleustonic plants can be disturbed by external factors (e.g. flooding). In this way, the succession is disrupted and brought back to an early stage. Also, pleustonic vegetation is influenced by seasonal changes in species combination and frequency. In conclusion, a classification of pleustonic assemblages is possible and useful if we disregard the initial stages and take into account that transitions between the units occur frequently and in any combination.

LANDOLT, E.

Acknowledgements. I am very grateful to Dr. Stephan G. Beck, Herbario Nacional de Bolivia, Cota-Cota, La Paz, and to Prof. Dr. Luis Eduardo Mora Osejo, Academía Colombiana de Ciencias Exactas, Physicas y Naturales, Bogotá, for their generous support in organizing the field trips in Bolivia and Colombia, respectively. Sincere thanks are due to Walter Lämmler, Zürich, who assisted on all three field trips and to Fidel Ernesto Poveda Gomez and Udo Schmidt-Mumm, Bogotá, who guided us professionally through parts of Colombia. I am also obliged to Anita Hegi for preparing the maps and for cultivating the collected Lemnaceae clones and to a referee who provided constructive criticism on the paper. I am very happy to dedicate this contribution to Frank Klötzli at the occasion of his 65th birthday. He travelled through many parts of the world studying the relation between vegetation and environmental conditions. Wetlands belong to his main interests. During his trips he always found time to collect living Lemnaceae species for my studies. I am greatly obliged to him for his kind and valuable cooperation.

References de la Sota, E.R. 1962a,b, 1963, 1964. Contribución de las Salviniaceae neotropicales, I-IV. Darwinia 12: 465-498; 499-513; 514-520; 13: 530-536. Eskuche, U. 1986. Bericht über die 17. Internationale Pflanzengeographische Exkursion durch Nordargentinien (1983). Veröff. Geobot. Inst. Eidg. Tech. Hochsch. Stift. Rübel Zür. 91: 12-117.

App. 1. Localities of the relevés. 007-162: Bolivia. 007-010: Beni, Laguna San José, 15 km NNE of Riberalta. 011-013: Beni, Laguna Tumichucua, 20 km SW of Riberalta. 014-023: Beni, Lagunas W of Riberalta. 024-025: Beni, Laguna Vista Allegre, Nueva Santa Elena. 026: Beni, Laguna Galilea, Nueva Santa Elena. 028: Beni, 10 km N of Sta. Rosa. 030, 032: Beni, Reyes. 033: Beni, Turrucuco, Reyes - Rurrenabaque. 034: Beni, Puerto Motor, N of Rurrenabaque. 035: Beni, 2 km S of Rio Colorado, N of Yucumo. 037: La Paz, 2 km S of Warizata. 3850 m. 040: La Paz, pass between Achacachi and Sorata. 4150 m. 101: Beni, 15 km NE of Yucumo. 105: Beni, 7 km E of San Borja. 109: Beni, La Pascane Grande, Est. de Biológica del Beni. 110: Beni, 19 km SW of San Borja. 111-115: Beni, Rio Yocuma near Santa Rosa. 116: Beni, Laguna Colorado near Santa Rosa. 118: Beni, 55 km S of Rurrenabaque. 119: Beni, 65 km S of Rurrenabaque. 120: Beni, 70 km S of Rurrenabaque. 121: Beni, 20 km E of Est. de Biológica. del Beni. 122: Beni, Rio Moseruna W of San Ignacio. 124-126: Beni, San Ignacio. 127: Beni, 40 km E of San Ignacio. 128-129: Beni, 45 km E of San Ignacio. 130: Beni, 50 km ESE of Trinidad, near Casarabe. 131-136: Santa Cruz, 5-25 km E of San Pablo. 137: Santa Cruz, 85 km S of Ascención. 138-139: Santa Cruz, 130 km S of Ascención, S of San Ramon. 140: Santa Cruz, 5 km S of San Julian. 141-142: Santa Cruz, S of Los Trancos. 143: Santa Cruz, Pailon. 144: Santa Cruz, 10 km N of Warnes. 145: Santa Cruz, 19 km N of Warnes. 146: Santa Cruz, 6 km NW of San Carlos. 148, La Paz, Puerto Perez. 149: La Paz, W of Huarina. 150: La Paz, Huatajata. 151-152: La Paz, Copacabana. 153-154: La Paz, San Pablo/Tiquina. 156-157:La Paz, Cota Cota, University. 159-161: La Paz, Laguna

Landolt, E. 1986. The family of Lemnaceae - a monographic study. Vol. 1. Veröff. Geobot. Inst. Eidg. Tech. Hochsch. Stift. Rübel Zür. 71. Landolt, E. & Zarzycki, K. 1994. Ecological field investigations of duckweed (Lemnaceae) in Argentina. Ber. Geobot. Inst. Eidg. Tech. Hochsch. Stift. Rübel Zür 60: 62-109. Libermann Cruz, M., Pedrotti, F. & Venanzoni, R. 1988. Le associazioni della classe Lemnetea del lago Titicaca (Bolivia). Idrobiologia 27: 377-388. Libermann Cruz, M., Pedrotti, F. & Venanzoni, R. 1991. La vegetación flotante (Clase Lemnetea) del lago Uru-Uru, Depto. Oruro, Bolivia. Ecología en Bolivia 17: 47-51. Pott, V.J. 1993. A familía Lemnaceae S.F. Gray no Pantanal (Mato Grosso e Mato Grosso do Sul). Brazil. Doctoral Thesis, Univ. Federal de Paraná, Curitiba. Schwaar, J. 1986. Gewässervegetation von Nordost-Uruguay. Ber. Deutsch. Bot. Ges. 99: 383-388. Schwabe-Braun, A. & Tüxen, R. 1981. Lemnetea minoris. Prodromus der europäischen Pflanzengesellschaften 4. J. Cramer, Vaduz. Wolek, J. 1997. Species co-occurrence patterns in pleustonic plant communities (class Lemnetea). Are there assembly rules governing pleustonic community assembly? Fragm. Flor. Geobot. Suppl.: 53-100.

Received 15 September 1998; Revision received 12 April 1999; Accepted 22 April 1999.

Jachcha Khota, Achocalla, 3750 m. 162: La Paz, Laguna Las Animas. 3900 m. 202-280: Colombia. 202: Cesar, Zapatosa. 204: Magdalena, 10 km S of Bosconia. 205-206: Atlantico, 5 km S of Malambo. 207: Atlantico, Lagos de Sabangrande. 208-209: Atlantico, Polonuevo. 210: Atlantico, La Isla de San José. 211: Atlantico, Santo Tomás, 5 km S of Sabanagrande. 212-213: Atlantico, South of Ponedera. 214: Atlantico, between Sabanagrande and San Tomás. 215-217: Atlantico, NE of Cuatro Bocas (NE of Tubara). 219: Atlantico, 5 km ENE of Luruaco. 220-221: Atlantico, 7-10 km W of Manati. 222-227: Atlantico, Embalse Guájaro, 0-7 km N of Auyamar. 228: Atlantico, 4 km S of Campeche. 229: Atlantico, N exit of Malamba. 230: Atlantico, 5 km S of Galerazamba. 231-232: Bolivar, 2 km NW of Arjona. 233: Bolivar, S exit of Arjona. 234, Bolivar, 10 km S of Arjona. 235: Bolivar, 3 km N of Gambote. 236: Bolivar, Gambote. 237: Bolivar, N exit of Arjona. 238: Bolivar, 2 km NW of San Cayetano. 239: Sucre, 5 km NNE of Ovejas. 241: Cordoba, 1 km SW of Cereté. 243-244: Cordoba, 1 km S of San Pelayo. 245-246: Cordoba, S of Guayabal. 247-256: Cordoba, 0-18 km S of Lorico. 257: Cordoba, W of San Bernardo del Viente. 258: Cordoba: Playa de San Bernardo. 259: Cordoba, S of Lorica. 260: Cundinamarca 17 km N of La Dorado. 261-263: Cundinamarca 0-4 km S of Tibito. 2550 m. 265-266: Cundinamarca Laguna de La Herrera. 267: Cundinamarca 2 km S of Funza. 268: Cundinamarca La Florida, Cota. 270: Cundinamarca, Bogotá, La Conejera. 271: Cundinamarca, Bogotá, Santa Maria del Lago. 272: Cundinamarca, Tocaima, 8 km SW of Berlin. 274: Huila, 1 km NW of El Juncal. 275: Huila, Laguna El Juncal. 277. Cundinamarca 5 km NE of Girardot. 279-280: Cundinamarca Laguna de Pedro Palo, Tena. 301-482: Argentina (see Fig. 1 in Landolt & Zarzycki 1994)