Rhynchospora alba

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Rhynchospora alba

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Cyperaceae
Genus: Rhynchospora
Species:
R. alba
Binomial name
Rhynchospora alba
Synonyms
  • Schoenus albus L.
  • Mariscus albus (L.) Gilib.
  • Scirpus albus (L.) Salisb.
  • Triodon albus (L.) Earw.
  • Phaecocacephalum album (L.) House
  • Dichromena alba (L.) J.F.Macbr
  • Rhynchospora luquillensis Britt.
  • Rhynchospora alba var. kiusiana Makino.
  • Rhynchospora alba f. laeviseta Gale

Rhynchospora alba, the white beak-sedge, is a plant in the sedge family,

mire ecosystem health.[5]

The species was first described by

Korean Peninsula.[3][8] Due to this large range, there is considerable variation between populations, and numerous varieties have been identified.[9][10] The plant has few uses, though it is used as an ornamental in the UK
.

Description

Rhynchospora alba is a

perennial herb between 10 and 50 cm in height,[2][11] though plants up to 75 cm tall can be found in North America.[3][12] The plant grows in tight clumps, meaning it is often difficult to distinguish individual stems.[3][10]

The plant consists of a single erect stem, which is three-angled and thin, usually 0.5–1 mm thick.[2][3][12] The leaves attached to the stem are three-ranked (in spirals around the three edges of the stem) and parallel veined, extending up to 15 cm in length [6], though none overtop the stem.[3] Each leaf is differentiated into a green or straw coloured sheath, which hugs the stem, and a grey/green blade, which is flat and slender (0.7–2 mm) and tapers to a blunt tip.[2][11] In some specimens, the margins of the blade are sparsely covered in hairs.[7][10] Unlike many sedge species, there is no ligule (outgrowths at the meeting of the blade and sheath).[3] At the base of the plant, the leaves have no blade, and only the sheaths are present.[2] These are often subtending a 10–20 mm bud, which will overwinter and grow a new plant in spring.[4]

While most Rhynchospora have large rhizomes (tuber-like stems below the soil surface), R. alba has very small rhizomes, or none at all, and very shallow root systems.[11] This reflects its different life history to many other sedges – R. alba loses all but the basal overwintering bud during the winter, while most other species retain and store nutrients in well-developed rhizome and root structures.[4]

Reproductive structures

Rhynchospora alba flowers in August,

anthers (each 1 mm in length).[2][15] The petals and sepals (perianth) are homogenous and highly modified, forming ring of 9–13 bristles with downward-facing barbs.[2]

After pollination the flower develops into an achene – a dry fruit that is indehiscent (it does not open at maturity) and contains a single seed.[13] This is composed of a 2 mm x 1 mm, egg-shaped achene body and the remnants of the style base of the flower, which forms a 1 mm beak-like structure called the tubercle.[12] The perianth bristles are also retained, and these are shorter than, or the same length as, the achene and tubercle combined.[2][3] The lengths of both the tubercle and perianth bristles are key characters for distinguishing R. alba from other Rhynchospora species.[12]

Similar species

White beak-sedge closely resembles a number of other sedges, including the brown beak-sedge (R. fusca) and large beak-sedge (R. macra).[3] It can be distinguished from other species by the reduced size of its rhizomes, the length of the tubercle and perianth bristles on the fruit, and the presence of downward facing barbs on the bristles.[2]

Etymology

The genus Rhynchospora derives from the Greek Rhynkos – "beak" and spora "seed".[10][12] This, along with the genus’ common name beak-sedge, refers to the long beak-like tubercle at the top of the achene fruit. This is characteristic to the entire genus and is often used for intra-generic classification.[12][15] The species name alba derives from the Latin albus, or white,[12] and refers to the white glumes surrounding each flower, which give the inflorescence its colour.

The species has multiple common names, the most common being white beak-sedge, again referring to the inflorescence colour and shape of the tubercle.[2] It is also known as white beak-rush, though this is misleading, as it is not in the rush family.

Habitat and ecology

Rhynchospora alba favours

dry deposition) and Sphagnum moss-dominated communities, where it is one of the few vascular plant species present.[4][5] Studies into nutrient and mass allocation by R. alba found the plant exhibits much higher rates of nutrient accumulation and loss across the growing season than in other sedges, which rely more heavily on storage and remobilising of nutrients in rhizomes.[4] This is likely related to the much lower levels of interspecific competition
experienced by R. alba in these bogs than other sedges in more grass-dominated environments.

It is also found in

peatlands alongside other sedge species such as Carex species.[2][5] It has a persistent seed bank, with seeds living up to five years.[16] It is therefore often an early re-coloniser in disturbed environments, where it can become the dominant species in so-called R. alba sedgeland.[17] It is much less dominant of more established communities, however, as it is less capable of outcompeting sedge species with more developed root and rhizome systems.[4][17]

Rhynchospora alba is wind-pollinated and wind-dispersed,[12][13] so has few close interactions with insect pollinators, but is a major food source for a number of bog-dwelling species, such as Paraphlepsius leafhoppers in the US.[18]

Distribution

Although most species of Rhynchospora are found in

Korean Peninsula.[2][8][11][19]

It is generally found at lower altitudes (below 850 m),[3] but has been found at higher altitudes at the southern edge of its range, for example in China and Puerto Rico.[10][11]

Taxonomy and systematics

Owing to the high

bog rushes (due to similarities in inflorescence) under the binomial name Schoenus albus.[6] This classification proved inaccurate, and Martin Henrichsen Vahl reclassified the species in 1805 as Rhynchospora alba, placing it in a novel genus that grouped species with a characteristic beak-like tubercle on the achene fruit.[7]

Rhynchospora alba (L.) Vahl is the current accepted species name for the white beak-sedge, but there has been considerable contention around its classification over the last 200 years

lectotype.[20]

Contention around Rhynchospora classification

The classification of R. alba has come under considerable scrutiny since Vahl's description, due to conflicting

Pleurostachys, with all other names either synonyms or sub-groups.[15] Kükenthal also split Rhynchospora into subgenera Diplostylae and Haplostylae, and this classification is still widely used today.[3][15]

The result of this contention is that many Rhynchospora species have numerous synonyms. Those for R. alba include Dichromena alba[24] and Phaecocacephalum album,[25] from attempts to rename all Rhynchospora. These synonyms were identified in monographs by Kükenthal and Gale,[10][15] as well as more recent studies by Kew's World Checklist of Selected Plant Families.[9]

Many varieties and forms of R. alba have also been described over the last two centuries.[9] Some have subsequently been described as new species – R. alba var. fusca was subsequently reclassified as R. fusca as it was found to have very different morphology.[26] Others, such as R. alba var kiusiana and R. alba f. laeviseta, are considered synonyms,[9] pending more work on the genetic structuring of the species.

Insights from molecular phylogeny

Before molecular data was more readily available, classification systems such as that of Kükenthal placed R. alba within Rhynchospora subg. Diplostylae based on its tubercle and bifid style.[15] How the tribe Rhynchosporae was related to other groups within the Cyperaceae was less clear, with Kükenthal suggesting they formed their own clade,[15] others suggesting they were part of the larger Cyperaceae tribe Schoenae.[21][27]

A recent molecular phylogeny suggests that Rhynchosporae are a separate but closely related clade to the Schoenae.[28] Molecular studies within the Rhynchosporae, however, reveal that Kükenthal's widely accepted classification holds less well – neither Haplostylae nor Diplostylae are monophyletic, and there appear to be multiple conversions between bifid and non-bifid styles throughout the genus.[21]

Surprisingly, the genus Pleurostachys (Group I) was also nested within Rhynchospora rather than sister to it.[21] Further study is required to confirm the position of Pleurostachys, but this indicates that Rhynchospora is not monophyletic, and reclassification of both genera may be necessary.

Uses

White beak-sedge is used very little by humans due to its favoured habitat of nutrient-poor acidic bogs,

restoration.[8]

Conservation status

Rhynchospora alba is currently assessed by

critically endangered in Croatia and has been reported as extinct in Hungary.[8]

There has been little study into the genetic structuring and threat status of the different varieties of Rhynchospora alba. As such, it is not known if regional population declines are eroding genetic and subspecies diversity, nor whether some sections of the species range are of greater conservation concern than others.

References

  1. doi:10.2305/IUCN.UK.2014-1.RLTS.T19618181A19620886.en
  2. ^ a b c d e f g h i j k l m n o p q Jermy, C; Simpson, D; Foley, M; Porter, M (2007). Sedges of the British Isles. B.S.B.I. Handbook No. 1. London: Botanical Society of the British Isles.
  3. ^ a b c d e f g h i j k l m Kral, R (2002). Flora of North America. Vol. 23. St Louis: Missouri Botanical Garden Press. pp. 230–239.
  4. ^
    JSTOR 3565365
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  5. ^
    S2CID 32046119
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  6. ^ a b Linnaeus, C (1753). Species Plantarum 1. p. 44.
  7. ^ a b c d Vahl, M.H. (1805). Enumerato Plantarum 2. p. 229.
  8. ^
    doi:10.2305/IUCN.UK.2014-1.RLTS.T19618181A19620886.en. {{cite journal}}: Cite journal requires |journal= (help
    )
  9. ^ a b c d Govaerts, R; Simpson, D.A. (2007). "World Checklist of Cyperaceae: Sedges".
  10. ^ a b c d e f g h i j Gale, S (1944). "Rhynchospora sect. Eurhynchospora in Canada, the United States and the West Indies". Rhodora. 46: 89–134.
  11. ^ a b c d e f g h Wu, Z.; Raven, P.H. Flora of China. Vol. 23. St Louis: Missouri Botanical Garden Press. pp. 1–515.
  12. ^ a b c d e f g h i McMillan, P.D (2007). "Rhynchospora (Cyperaceae) of South Carolina and the Eastern United States". Biota of South Carolina. 5: 1–269.
  13. ^ a b c d e Goetghebeur, P. (1998). "Cyperaceae". In Kubitzki, K.; Huber, H.; Rudall, P.J.; Stevens, P.S.; Stuetzel, T. (eds.). The Families and Genera of Vascular Plants. Berlin: Springer-Verlag. pp. 141–190.
  14. S2CID 30428671
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  15. ^ a b c d e f g h Kükenthal, G. (1949–1951). "Vorarbeiten zu einer Monographie der Rhynchosporoideae". Bot. Jahrb. Syst. 74, 75: 375–509, 90–115, 273–314, 451–497.
  16. S2CID 1782787
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  17. ^
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  18. S2CID 90424788
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  19. ^
    doi:10.15468/39omei. {{cite journal}}: Cite journal requires |journal= (help
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  20. JSTOR 4135509
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  21. ^
    S2CID 13432358
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  22. ^ Nees von Esenheck, C.G.D. (1835). "Uebersicht der Cyperaceengattungen (Synopsis Generum Cyperacearum)". Linnaea. 9: 282–297.
  23. ^ Bentham, G.; Hooker, J.D. (1883). Genera Plantarum. London: Lovell Reeve & Co. p. 1041.
  24. ^ MacBride, J.F. (1929). "The Status of Rhynchospora: Some Peruvian Sedges". Publication of Field Museum of Natural History, Botanical Series. 4 (7): 165–66.
  25. JSTOR 2992937
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  26. ^ Aiton, W.T. (1810). Hortus Kewensis. p. 127.
  27. doi:10.1071/SB9950125
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  28. ^ Mussaya, A.M.; Simpson, D.A.; Verboorn, G.A.; Goetghebeur, P.; Naczi, R.F.C.; Chase, M.W.; Smets, E. (2009). "Phylogeny of Cyperaceae Based on DNA Sequence Data: Current Progress and Future Prospects". Botanical Review. 75 (1): 20–22.

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