Taxonomy of Cyperus section Arenarii (Cyperaceae)

Henry Väre, Ilkka Kukkonen

Cyperaceae is one of the largest family of vascular plants, with 4000 to 5000 species in 70 to 105 genera. Cyperus L. (subfamily Cyperoideae, tribus Cypereae) is the second largest genus after Carex in the family, with about 600 species included in the most recent monograph by Kükenthal in 1936. He had a broad species concept, and a number of new species have been described later.

Nees already in 1837 applied sectional division in Cyperus by creating eight sections. Aristati, Compressi, Irioidei (= Iriae Kunth), Alopecuroidei (= Alopecuroidei Chermezon), Mariscoidei, Allagostachyi, Capituligeri and Hymenolepides. The monophyly of the sections is unresolved so far, and many alternative sectional solutions have been proposed. Section Arenarii, first presented by Kunth and validated by Jaub. & Spach is here considered to represent a natural unit.

Type of Cyperus falcatus Nees, [Sudan], Dongola, in desertis ad Ambakohl frequens., Aug. 1820-26. G. Ehrenberg.

The total area of the section extends from the Black Sea and the Mediterranean Area (C. capitatus) around Africa along the coastal sands (C. crassipes ssp. crassipes and C. crassipes ssp. maritimus), and eastwards to India and Sri Lanka (C. arenarii). Towards inland the members of the section extend into areas surrounding the deserts, and some have been able to penatrate even the most arid parts of Sahara, the Arabian Peninsula and Iranian high plateau. The greatest species diversity appears to concentrate into regions around the Red Sea in N.E. Africa and the Arabian Peninsula.

Most species are psammophytic, adapted to survive in hot dry deserts, and exhibit convergent morphology in characters which prohibit water loss. Such common features include thick cuticula in all parts of the plant, glaucescent colouration, canaliculate leaves minimising evaporation, and reduced inflorescence structures. The long creeping rhizome, for example in C. eremicus Kukkonen and in C. macrorrhizus Nees is buried deep in the sand, the structure of the roots when thickly tomentose, are adaptations to the extreme arid conditions also. Tomentose roots hold effectively moisture. Species colonizing moving sand dunes are adapted to be occasionally buried by sand. Spreading is enabled by large, flat and winged nuts at most adverse deserts. Some other species are less distinctly adapted to the aridity. For example, C. conglomeratus Rottb.s. str. have short rhizome and small nuts, and is, evidently, better suited for seed bank strategy.

Morphological examination of herbarium samples revealed many undescribed species, and numerous synonymes within described ones. Annual species have not so far been described in section Arenarii. Such are known in other sections, and are present in Arenarii also. The current project aim to clarify nomenclature, to typify published names, to produce a phylogenetic analysis, and finally to prepare a monograph on the section. Currently we recognize 23 species and two subspecies.