Commelina singularis Vell., Fl. Flumin.: 31. 1829.

Pellegrini, Marco Octavio de Oliveira & Forzza, Rafaela Campostrini, 2017, Synopsis of Commelina L. (Commelinaceae) in the state of Rio de Janeiro, reveals a new white-flowered species endemic to Brazil, PhytoKeys 78, pp. 59-81 : 66-68

Commelina singularis Vell., Fl. Flumin.: 31. 1829. Fig. 6

Lectotype

(designated here). [illustration] Original parchment plate of Flora fluminensis in the Manuscript Section of the Biblioteca Nacional do Rio de Janeiro [mss1095062_080] and later published in Vellozo, Fl. flumin. Icon. 1: t. 76, pro parte, flowers and inflorescence only. Epitype (designated here). BRAZIL. Rio de Janeiro: Rio de Janeiro, Área do Jardim Botânico do Rio de Janeiro, fl., fr., 21 Dec 1995, J.A. Lira Neto 194 (RB 2ex, barcode RB00685321!).

Accepted name.

Tripogandra diuretica (Mart.) Handlos.

Taxonomical notes.

Vellozo’s plate for C. singularis (1831: t. 76) shows a creeping plant with eudicot-like leaves (net-veined and a single apparently trifoliate leaf), not identifiable as any known species of Commelinaceae . Nevertheless, the inflorescence type (Fig. 6A, C ), details of the androecium (Fig. 6B, D ), and the morphological description of six dimorphic stamens, three of which are staminodial - " Stamina sex, quorum tria nectaria mentiuntur " - ( Vellozo 1829), consistently allows this name to be associated to the genus Tripogandra Raf. Another remarkable feature of Vellozo’s plate is the gynoecium, which is illustrated with a very short and slightly curved style (Fig. 6B ). This feature distances C. singulars from the genus Commelina where the style is long and sigmoid, bringing it closer to Tripogandra . The leaves illustrated by Vellozo belong to the genus Polygonum L. ( Polygonaceae ), which usually possesses white to pink to lilac flowers, and occurs in the same marshes as T. diuretica . This confusion is apparently common in Brazilian herbaria, where Polygonum specimens are commonly misidentified as commelinaceous taxa (Pellegrini pers. obs.).

Vellozo (1829: 31) also mentions that C. singularis is found growing in slow-water environments - " Aquis stagnantibus, et confluentibus habitat " -. Only T. diuretica and T. warmingiana (Seub.) Handlos occur in the state of Rio de Janeiro; the first being very common, extremely variable in size and flower morphology, and normally occurring in marshy areas; the second being very rare, uniformly small in size and flower morphology, and occurring in drier areas ( Pellegrini et al. 2013). Thus, C. singularis is here regarded as a synonym of T. diuretica . In accordance to the Code ( McNeill et al., 2012, Art. 9.8), in order to avoid future confusions and to fix the application of this name, we herein designate an epitype for C. singularis .

Figures

Figure 6. Commelina singularis Vell. A-B Original plate of Vellozo's C. singularis: A line drawings of habit, inflorescence and floral characters B detail of floral characters. C, photos of a natural population of Tripogandra diuretica from the Jardim Botanico Rio de Janeiro, RJ: detail of the inflorescence, showing flowers with white corolla D-E photos of T. diuretica from the municipality of Petropolis, RJ: D detail of floral characters of a flower with lilac corolla E detail showing the leaves (note the parallel venation characteristic of the species) SS sterile stamens; FS fertile stamens; Gy gynoecium. Photo of C. singularis plate from Biodiversity Heritage Library; All field photos by M. O. O. Pellegrini.