Maguire, Bassett. 1972. The botany of the Guayana Highland--part IX. Mem. New York Bot. Gard. 23: 1-832.
Cyperaceae
Fig 6A, B.
Scirpus cephalotes L., Sp. PI. ed 2, 1: 76. 1762. Type from West Indies.
Schoenus cephalotes (L.) Rottboell, Descr. Icon. Rar. PI. 61, t. 20. 1773. Based on Scirpus cephalotes L.
Dichromena schoenus Macbride, Publ. Field. Mus. Bot. 11: 6. 1931. New name for Scirpus cephalotes L., not Dichromena cephalotes Britton, 1888.
Rhynchospora conica Desvaux ex Hamilton, Prodr. FI. Ind. Occid. IS. 1825. Type. “Herb. Prof. Desv. Cayenne.” (n v, fide Kükenthal 1950).
Rhynchospora cephalotes Vahl var angustifolia Uittien, Rec. Trav. Bot. Neerl. 30: 188. 1933. Syntype. Suriname, Gran Rio, Hulk 346 (U); M. Wilhelmina, Stahel 585 (U). Rhynchospora cephalotes Vahl var imeriensis Kükenthal, Bot. Jahrb. 75: 124. 1950. Type. Holt & Blake 486 (B, NY) from Salto de Huá, Serra Imeri, Brazil.
[Rhynchospora imeriensis R. Gross ex Kükenthal, Bot. Jahrb. 75: 124. 1950. Invalid name cited in synonymy.]
Type. West Indies, Herb. Linn, sheet no. 71.56 (LINN).
The three species, R. cephalotes, R. cephalotoides, and R. Comata, have often been confused due to the difficulty in making taxonomic separation among them. Differences among the three plants observed on over 340 specimens are shown in Table I.
The general means of separating R. comata from R. cephalotes has been based on the pubescent leaves and culms, and inflorescence of both terminal and lateral open panicles bearing peduncled spikelets in R. comata in contrast to the glabrous leaves and culms, and a terminal head-like inflorescence with sessile spikelets in R. cephalotes. The separation in this manner may sometimes be obscured, since in R. comata leaves occasionally become glabrescent, while in R. cephalotes inflorescences may either be lobed or have lateral ones. An amendment has been made in Table I to make the separation on vegetative characters more accurate. The most dependable segregation between R. comata and R. cephalotes can be made by the achenes as shown in Table I. Particularly, the quite different patterns of achene epidermis are consistent and thus warrant a definite distinction. In R. cephalotes the yellowish-brown achenes are conspicuously foveolate with longitudinally oblong to elliptic pits, whereas in R. comata the deep-brown or reddish-brown achene surfaces are rather obscurely cancellated with obtusely pentagonal or hexagonal isodiametrical small cells, and the cuticle has no depressions at all. Furthermore, in R. cephalotes the hypogynous bristles are flattened for the entire length or at least in the basal portion with narrow brown edges, which are scabrous with patent spinules, while in R. comata the bristles are slenderly capillary without flattened edges and are scaberulous with minute adpressed spinules.
The inflorescences of R. cephalotes frequently become viviparous not producing mature achenes, a phenomenon so far never observed in R. comata. The Linnaean type of Scirpus cephalotes, on which R. cephalotes was based, is the specimen No. 71-56 (LINN), and is reportedly from the West Indies, whereas R. cephalotes is absent except in Trinidad and Tobago. But the type specimen bearing a large viviparous head matches exactly R. cephalotes from Central and South America, demonstrating that the name, R. cephalotes, is correctly applied to this taxon.
The type specimen of Schoenus comatus, on which R. comatus rests, is not extant. The type collection was made by Sellow in “Brasilia meridionalis,” where the occurrence of R. comata is very doubtful. The descriptions of R. comata given by Kunth and Böckeler, who must have examined the Sellow’s specimen (B), however, clearly designate such typical features of R. comata as open panicles and pubescent leaves. I, therefore, follow the traditional application of the name, R. comata.
Rhynchospora cephalotoides of the West Indies is here regarded to be a distinct species. Possibly because of its much reduced inflorescences R. cephalotoides was treated by Kükenthal as a variety under R. cephalotes. However, its indistinctly cancellated achenes and deeply green leaves that are often puberulent show no immediate taxonomic affinity between R. cephalotoides and R. cephalotes, but suggest a rather closer relation with R. comata. Nevertheless, the compressed hypogynous bristles in association with definitely smaller achenes in R. cephalotoides sharply separate it from R. comata. The geographic range of R. comata is also independent of those of the two relevant species.
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