The genus Orobanche in Suffolk, a review of past records and taxonomy

T H E G E N U S OROBANCHE

IN SUFFOLK, A R E V I E W O F FAST

RECORDS AND

TAXONOMY

MARTIN SANFORD

B r o o m r a p e s , the genus Orobanche, are a fascinating group o f parasitic plants w h i c h , because o f their reduced m o r p h o l o g y , have often confused botanists. T h e i r peculiar colours and w e i r d , almost orchid-like appearance p r o v i d e a mysterious appeal. T r a d i t i o n a l l y they have been classed as a f a m i l y , the Orobanchaceae, but there is no clear distinction between them and the Scrophulariaceae, w h i c h also contains parasitic and semi-parasitic species. I n d e e d , D . A . W e b b (in T u t i n et al, 1964-1980) writes 7 / is impossible to delimit this family satisfactorily from the Scrophulariaceae, and it would seem that nothing but tradition maintains its separate status'. A s i n other parasitic groups the lack o f leaves and the morphological changes that have evolved as a result o f the specialised relationship w i t h the host have given taxonomists many problems. Despite the reduction i n parts, many species show great Variation in size, c o l o u r , degree of hairiness a n d even floral m o r p h o l o g y so that accurate d e l i m i n a t i o n of species is also difficult.

This is particularly true o f the O. minor aggregate i n w h i c h we can see partial speciation as a result o f inbreeding and adaptation to particular hosts and perhaps also to particular habitats (e.g. var. maritima).

T h e intrinsic taxo n o m i c difficulties o f this genus are greatly increased by the fact that many o f the i m p o r t a n t characters are not easily observed i n dried specimens. A s John A c k e r o y d (1991) puts i t , h e r b a r i u m specimens of Orobanche can at worst 'look like a Bombay Duck withflowers'\ M o s t o f the species are herbs w h i c h lack Chlorophyll and rely t o t a l l y o n r o o t connections w i t h the host plant for nutrients. T h e y produce very large quantities o f m i n u t e seeds w h i c h despite having v i r t u a l l y n o f o o d reserves and g r o w i n g tissues are able t o lie d o r m a n t for many ( 1 5 - 2 0 ) years. D o r mancy is b r o k e n o n l y w h e n the seed is i n close p r o x i m i t y t o roots o f a suitable host and w h e n temperature and moisture content o f the soil is correct. M o s t B r i t i s h species show a southern d i s t r i b u t i o n suggesting that t h e i r ränge is l i m i t e d by climatic factors. I t seems l i k e l y that soil temperature effects o n seed g e r m i n a t i o n are i m p o r t a n t in l i m i t i n g their spread.

I n w a r m e r climates species such as O. ramosa and O. crenata are serious agricultural weeds o f legume crops. O. crenata has recently been recorded f r o m several sites i n Essex and this attractive, 'carnation-scented' species should be l o o k e d for in S u f f o l k especially i n B r o a d Bean fields. R u m s e y and Jury (1991) suggest 'The climatic changes experienced recently, coupled with more frequent Faba bean crop cultivation, may result in the more frequent occurrence and establishment of this species in the British Isles. It could become a major and serious weed species in the 2Ist Century'.

Some species are restricted to a particular host plant or host f a m i l y while others such as O. minor are quite catholic and can parasitise a wide ränge o f plants f r o m d i f f e r e n t families. H o s t preferences vary w i t h i n the ränge of the plant. M a n y o f the B r i t i s h Orobanche species are reaching the n o r t h e r n edge

Trans. Suffolk

Nat. Soc. 28 (1992)

THE GENUS OROBANCHE

IN SUFFOLK

35

of their ränge and are far more host specific here than they are further south.

For instance, the Purple Broomrape, O. purpurea is restricted to Yarrow (.Achillea millefolium) in this country, but in Greece and Turkey it can be found on several other composites. At present, apart from occasional Problems with O. minor on clover, none of the British species parasitise economic crops in serious proportions, but a change to a warmer climate could expand their host ränge. What we now consider as attractive rarities might well become common weeds!

It can often be very difficult to decide which plant is the host without actually digging up plants to follow root connections. Chater (1985) gives a cautionary tale on the dangers of assuming the plant nearest the Broomrape is the host. His example of an Orobanche plant growing beside a concrete post with no other plant nearby illustrates how easy it is to jump to conclusions about the host without hard evidence.

Rumsey & Jury (1991) have provided an excellent account of the British species of Orobanche which has greatly clarified the taxonomy of the group and stimulated this paper on the Suffolk records.

Orobanche ramosa L. Branched Broomrape, Hemp Broomrape This species is now extinct in the British Isles, but occurred quite frequently as a casual weed of Hemp (Cannabis sativa) crops when it was grown commercially in East Anglia during the 18th and early 19th centuries. Hemp cultivation started in Saxon times and was probably more widespread in the warmer climate of the Middle Ages; it seems likely that O. ramosa was also more common then, but without written records this can only be conjecture.

Young (1813) records the main Hemp growing area in Suffolk as a strip some ten miles wide from Beccles to Eye. In fact Hemp cultivation spread further west into the Valley of the Little Ouse and over most of East Suffolk (Evans, 1988). Unlike most crops, which were grown in rotation, Hemp was often sown every year on the same land. Young notes a piece of land at Hoxne which had been used for Hemp for seventy years. The preferred soil was old meadows and low bottoms near rivers which were prepared carefully with much manure. Seed was sown as soon as spring frosts had ceased and the crop was ready for pulling by the beginning of August. Although the returns from this crop were high, it was labour intensive both in growing and retting to produce the fibre. By the mid-19th Century Raynbird (1849) reported that the crop was no longer grown.

Galpin (1888) records O. ramosa as 'Formerly not uncommon on Hemp and Galeopsis tetrahit', but notes that the Rev. E. A. Holmes failed to find it on Hemp grown 'some years ago' by Lord Waveney at Flixton (near Bungay).

If, as the English name 'Hemp Nettle' suggests, Galeopsis was once a weed of Cannabis crops it is likely that records of O. ramosa on Galeopsis are simply errors in identification of the host plant.

Hind (1889) gives records from near Beccles (-1724 J. Sherard in Dill. Ray & -1836 G. R. Leathes in Hb. J. D. Salmon), Mettingham (a specimen in Sir John Cullum's herbarium is labelled In füll blossom amongst hemp 31st Trans. Suffolk Nat. Soc. 28 (1992)

36 Suffolk Natural History, Vol. 28 August, 1790. My friend Mr. Woodward conducted me to th this plant grew'), near Bungay (specimen in British Museum coli. D. Stoc -1839, possibly from Earsham or Geldeston on the Norfolk side of the Waveney) and Brome (this should be Broome near Bungay, just over the Waveney in Norfolk, specimen in British Museum coli. T. J. Woodward Ist Sep. 1785).

O. purpuren Jacq. Purple Broomrape, Yarrow Broomrape

This very rare species is listed in the British Red Data Book (Perring & Farrell, 1983); most British sites are on cliff-tops or near the sea.

The recent discovery of a colony of this species at Lakenheath Cemetery (TL7282) is a most exciting addition to the Suffolk Flora. One spike was found by Mr. L. Flack, the groundsman, in 1990 and identified as O. purpurea by the late Marg Rutterford. This is thefirstconfirmed record o this species in the County (see Simpson, 1983). In 1991 more than 20 spikes were found at the original site and two plants were found in another part of the cemetery. Mr. Flack informs me that the turf on the site has been created from old grassland originally cut by scythe and he has not sown new grass or imported turf from elsewhere.

Records from Mariesford (N. Cracknell, 1932) and Farnham (E. Rowling, 1898) are probably confusions with purple-flowered forms of O. minor, they lack voucher material and must be regarded as doubtful.

The record from Cockfield mentioned in Hind (1889) is from a specimen provided by Dr. Babington growing in aflowerpotin his greenhouse in 1888.

This peculiar fasciate specimen is still in Hind's collection at Ipswich Museum, there are noflowersand it is impossible to see how it was identified as 'O. caerulea'.

O. rapum-genistae Thuill. Greater Broomrape

At one time this was the most widespread and frequently encountered species of Orobanche in Britain (Rumsey & Jury, 1991). For reasons whic are not yet apparent it has undergone a dramatic decline. The host plants, Broom and Gorse, are still very common and it seems likely the losses are due to climatic change rather than habitat loss. However, the species seems to occur only where the host plant is frequent and the destruetion of many tracts of heathland with large stands of Broom may have been significant. It is also possible that the cessation of the old tradition of cutting Furze and Whin may have resulted in a change in the age strueture with older, more woody plants predominating. Decreasing use of commons and heaths for stock might also mean the roots of these shrubs became less accessible to Broomrape seed. Since the advent of Myxomatosis in the 1950s, lack of grazing from Rabbits has caused heathlands to become much more overgrown which may also have hindered establishment of Broomrapes. Severe winters, such as that of 1962/3, can destroy the host plants and cause the loss of isolated colonies.

In the 19th Century this species was still quite widespread in the County, Trans. Suffolk Nat. Soc. 28 (1992)

T H E G E N U S OROBANCHE Orobanche rapum-genistae

37

IN S U F F O L K

(all p r e - 1 9 8 0

records)

though by no means common. There are specimens in the herbarium at Ipswich Museum from Fakenham (coli. W. M. Hind 23 June, 1882) and Bawdsey (coli. D r . C. Babington). Surprisingly, for a parasite of Broom and Gorse, the pattern of old records does not show an association with the major areas of heathland on the Sandlings and in Breckland. This may be due to the higher incidence of ground frosts in these areas which could have prevented germination of the Orobanche.

It still occurs, though in reduced numbers, at one site in the County. This is on the coast in an old stand of Broom which is in danger of inundation from the sea and it may not last much longer.

The record for Haverhill in Simpson (1982) is an error for O. elatior. H. Jenner found O. rapum-genistae at Herringfleet in the 1950s. It was seen at Tiger Hill, Bures in the 1970s, but has not been seen since then (pers. comm.

R. Ford). It also occurred at Sutton Tips in the 1970s; there are still suitable stands of Broom at this site. The species is perennial and can survive for long periods even when conditions are unfavourable, all old sites should be searched in case it has survived unnoticed.

O. alba Stephan ex Willd. Thyme Broomrape, Red Broomrape Rumsey & Jury (1991) point out that this species has only been found parasitising Thymus in Britain, records from other hosts have all proved to be

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Suffolk Natural History, Vol. 28

O. minor. H. J. Boreham's 1953 record from Bury St Edmunds on Ground Ivy (Glechoma hederacae) (Simpson, 1982) can be dismissed.

O. caryophyllacea Sm. Clove-scented Broomrape Rumsey (1985) suggests Suffolk records of this species are confusions with O. rapum-genistae. No specimens were collected by C. T. Giles of the plants found at Cläre apparently growing on Lady's Bedstraw (Galium verum) (Giles, 1951); it seems the identification was based on the assumed host rather than the Broomrape itself. As O. elatior was found at the same site, it is likely it was simply this species growing some distance from Centaurea and assumed to be parasitising Galium.

There are no specimens to support the records from Hawstead, Semer and Sudbury in Hind (1889), and given the very restricted native distribution of this species it seems likely these were also errors for other species.

O. elatior Sutton. Tall Broomrape This species is now quite scarce in the County, it has lost most of its sites in E. Suffolk (v.c. 25) and there are only a few left in the west of the County. It still

Orobanche

Trans. Suffolk Nat. Soc. 28 (1992)

elatior

T H E G E N U S OROBANCHE

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occurs in the disused Chalk Pit at Little Blakenham now managed as a SWT Reserve (pers. comm. Mrs. P. Gondris). There is an excellent protected roadside verge at Westley near Bury St. Edmunds where it grows in abundance and it has also been seen in recent years on verges around Cl채re.

In the King's Forest it can be seen in most years around Wordwell. It has never been common in Suffolk, like many Broomrapes it is essentially a southern species; here it is getting near to the northern limit of its r채nge and it is more dependent on warm south-facing slopes and sheltered roadside verges. It is always found parasitising Greater Knapweed (Centaurea scabiosa) and its distribution is largely limited by the frequency of this host.

The Knapweed is nearly always found on chalky soils and it is frequently found on exposed chalk in quarries and pits. It also occurs on well-drained crag soils in East Suffolk and, although there are 19th Century records of O. elatior at Chillesford, Sudbourne and Sutton and one from 1949 at Hollesley, it now seems to have disappeared from this area.

Rumsey & Jury (1991) suggest that the species is decreasing towards the western and northern extremities of its r채nge, possibly for climatic reasons.

As the host plant is still quite frequent it is possible that global warming may reverse this trend.

O. artemisae-campestris Vaucher ex Gaudin (O. loricata) Reichenb.

Oxtongue Broomrape, Picris Broomrape This is a very scarce plant restricted to W. Sussex, E. Kent and the Isle of Wight; it is protected under schedule 8 of the Wildlife & Countryside Act 1981. Pale forms of O. minor, especially those apparently parasitising Picris ssp. (usually var. compositarum) are often mistaken for this species. There is considerable morphological overlap between the two species and any records should be confirmed by an expert.

None of the records cited in Simpson (1982) are reliable. Records from Whatfield (1931) and Semer (c. 1933) were made by the enthusiastic, but untrained, Ronald Burn. B. D. Jones' record from Sicklesmere (1952) seems to be based on identification of the host, which was Hawkweed Oxtongue (Picris hieracoides), rather than examination of the Broomrape itself.

There is a record in Hind (1889) of a specimen of O. picridis' in the herbarium of Edmund Skepper collected in 1862 at Great Welnetham. F. J. Rumsey (pers. comm.) found plants of O. minor near the rake factory at Little Welnetham in 1989 with pale flowers and hairy stamen bases which closely resembled this species.

O. minor Sm. Common Broomrape, Lesser Broomrape This is the only widespread species in Suffolk, it has been found on a wide r채nge of hosts, mainly from the clover (Leguminosae) and Daisy (Compositae) families. Petch and Swann (1968) record it in Norfolk on 'clover, both wild and cultivated, making it difficult to grow this crop in certain fields\ Flowering usually occurs in July, though it can be any time between May and September. Repeated introduction with fodder crops has meant that any Trans. Suffolk Nat. Soc. 28 (1992)

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Suffolk Natural History, Vol. 28 Orobanche minor

'native' distribution pattern has been obscured. It was first recorded in Suffolk in 1805 by George Crabbe on Clover at Orford. Despite being a common plant it was not described as a separate species until 1797 and for this reason it was not recorded by Sir John Cullum in his journal (1772-1785) though he did find 'O. major'. Many 19th Century records give Clover as the host; it had been grown throughout the County as part of the crop rotation for many years and this must have aided the spread of O. minor.

Rumsey and Jury (1991) describe four varieties: - flava, maritima, compositarum and minor. Only the last two have been recorded recently from Suffolk. The distribution of these two varieties and of the yellow-flowered partial albinos of var. minor is shown on the map.

Var. compositarum is distinguished by its narrower (3.5-5.0mm diameter), paler, sub-erect flowers. Its hosts are usually composites especially Hawksbeards (Crepis spp.), but it can also be found on Common Cat's Ear (Hypochoeris radicata), Musk Thistle (Carduus nutans) and the garden shrub Ragwort Brachyglottis 'Sunshine' (=Senecio greyi auct.). There is a British record of it growing on Alexanders (Smyrnium olusatrum). This plant is quite frequent along the Suffolk coast and is increasing its ränge inland; Broomrapes found growing near Smyrnium should be examined to see if there are root connections.

Trans. Suffolk Nat. Soc. 28 (1992)

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There are no specimens of var. compositarum at Ipswich Museum, but in the herbarium at Norwich Castle Museum there is an excellent specimen collected by the late Ted Ellis at Brandon in 1954 where it was growing on the rare Field Wormwood (Artemisia campestris)\ Interestingly, there is a specimen of compositarum at the British Museum, also found growing on A. campestris, collected by W. G. Clarke at Northwold in Norfolk in 1922.

There are three Suffolk specimens of this variety at the British Museum; Felixstowe (H. Trimen, 1869), 'Sandhills at Thorpe near Aldeburgti (A. Bennett, 1901) and Freckenham 'on Crepis virens' (Pugsley, 1931). Rumsey and Jury (1991) remark 'It would seem to be most frequent on sandy soils in Surrey, East Anglia and in coastal areas elsewhere' and suggest it is probably under-recorded. Recently I have seen this variety at Barton Mills where it was abundant on a stand of Shrub Ragwort Brachyglottis 'Sunshine'. Edgar Milne-Redhead found it in his garden at Nayland in 1990 (det. J. J. Heath) with no obvious host nearby.

Var. minor seems to be what remains when the extremes shown by var.s compositarum, maritima and flava are removed. I can see little justification in providing this additional, repetitive varietal epithet 'by default'. Most plants of O. minor I have examined in Suffolk match this taxon. It is most frequently found on roadside verges, usually parasitising legumes, but can also occur in large numbers as a garden weed on Shrub Ragwort (Brachyglottis 'Sunshine') and rarely on other hosts such as Foxgloves or greenhouse Geraniums. It appears to be evenly distributed over the County but shows some preference for well-drained, calcareous soils. Plants vary greatly in size (probably as a result of host vigour) from tiny spikes only a few cm. high to tall specimens over 50cm. A specimen in Hind's herbarium found at Troston in 1892 growing on 'Lathyrus sylvaticus' measures 66cm.

There are two old records of 'O. maritima (=var. maritima) from Suffolk.

Simpson (1982) includes a record from Aldeburgh in 1912 made by the Botanical Exchange Club. The other is from Lowestoft where a record of 'O. amethystea' was made by J. A. Wheldon c. 1900.

One form of O. minor which is of special importance to Suffolk is a yellowflowered 'albino' found mainly in the Sandlings in a restricted area around Sudbourne, Chillesford and Thorpeness. At one site in Sudbourne the plants are protected on a roadside nature reserve, here they appear to be growing on Musk Thistle (Carduus nutans). It is possible that with self-fertilisation all the plants in this area have arisen from one seed source which has perpetuated the mutation. Albinism is not a selective disadvantage for a parasite which does not rely on pigments for its nutrient supply. Yellow-flowered plants have been known in the area for a long time, there are herbarium specimens in Ipswich Museum collected from a 'Cloverfield nr Aldborough' in 1854. Peter Lawson collected a specimen growing on Common Cat's Ear (Hypochoeris radicata) from a lawn at Thorpeness in 1984. They have also been found in the Breck, there is a specimen in the BM collected at Mildenhall by T. A. Preston in 1888 and Mrs E. Hyde found it at Barton Mills in 1990.

The colour is a result of partial albinism, the normal brownish/purple shade being caused by anthocyanins which, when absent, (probably as a

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Suffolk Natural History, Vol. 28

result of a Single gene mutation) leave more stable yellow anthoxanthins. In all other respects it resembles typical O. minor. In the past it has been recorded as var. lutea Tourlet or var. flava Regel. Rumsey & Jury (1991) have pointed out that plants of this variety from the Channel Islands and from Glamorgan Docks also differ from normal minor in the smaller, clumped spikes and suggest this morphological difference is not an environmental modification.

O. hederae Duby. Ivy Broomrape This species closely resembles O. minor-, it can be distinguished from minor by the distally pinched flowers which extend over most of the stem and the clump of unopened flowers at the top of the spike. It parasitises members of the Ivy family (Araliaceae) particularly the Atlantic form of Ivy (Hedera helix ssp. hibernica) and its garden cultivar H. 'Hibernica'; the native ränge follows the Atlantic coastal distribution pattern of this Ivy. I have not found any definite records of this species from Suffolk. The specimen collected by J. Atkins at Felixstowe in 1909 which Simpson (1982) gives as the first record has been examined by F. J. Rumsey and he thinks it is probably O. minor. O. minor can also parasitise Ivy which means that records based simply on the host may not be O. hederae. I have no further details of the records of O. hederae from Gisleham Rectory (Goddard, 1939) and Felixstowe (Simpson, 1950), but without specimens I would suggest they may well also be errors for O. minor.

Acknowledgements I would like to thank all those who have sent in Orobanche records or have contributed details on sites.

References Ackeroyd, J. (1991). Higher Plants Wildlife Report. British Wildlife, 2: 314.

Chater, A . O. (1985). Orobanche Hosts - A Cautionary Tale. BSBI News, 42: 10.

Evans, N. (1988). The Linen Industry.-in D y m o n d , D. & Martin, E. (1988).

An Historical Atlas of Suffolk. Suffolk County Council & Suffolk Inst.

Arch & Hist., Bury St. Edmunds.

Galpin, F. W. (1888). An account of the Flowering Plants of Harleston.

Bartlett & Co., London.

Giles, C. C. T. (1951). Proceedings - General Excursion 7th July, 1951.

Trans. Suffolk Nat. Soc., 7: lxiv.

Hind, W . M. (1889). The Flora of Suffolk. Gurney & Jackson, London.

Petch, C. P. & Swann, E . L. (1968). Flora of Norfolk. Jarrold.

Raynbird, W. & H . (1849). On the agriculture of Suffolk. Longman.

Rumsey, F. J. (1985). Orobanche caryophyllacea Sm. in North Wales.

Watsonia, 15: 277.

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Rumsey, F. J. & Jury, S. L. (1991). An account of Orobanche L. in Britain and Ireland. Watsonia, 18: 257-295.

Simpson, F. W. (1982). Simpsons Flora of Suffolk. Suffolk Naturalists' Society, Ipswich.

Simpson, F. W. (1982). Doubtful records of Orobanche purpurea. Jacq.

Trans. Suffolk Nat. Soc., 19: 371-372.

Tutin, T. G . et al., eds. (1964-1980). Flora Europaea, 1 - 5 . Cambridge.

Young, A . (1813). General view ofthe Agriculture ofthe County of Suffolk.

Sherwood, Neely and Jones, London.

Martin N. Sanford Suffolk Biological Records Centre, Ipswich Museum, High Street, Ipswich, IP1 3 Q H

Trans. Suffolk Nat. Soc. 28 (1992)

Plate 7: Purple Broomrape (Orobanche purpurea) at Lakenheath Cemetery. (p.36).

Plate 8: Common Broomrape (Orobanche minor) is the only widespread broomrape in Suffolk. (p. 39).

Plate 9: Common Broomrape (Orobanche minor): yellow form at Sudbourne. (p. 40).