Callianthe clarkei Dorr 2025, sp. nov.

1.Callianthe clarkeiDorr sp. nov. Fig. 1 Diagnosis. Differs from Callianthe sylvatica (Cav.) Dorr in having broadly ovate (versus ovate or ovate-oblong) leaf blades with acute or broadly acute (versus acuminate) apices, axillary flowers (2 –) 3 per axil (versus solitary or paired), peduncles ± equal to (versus exceeding) petioles in length and petals 1.2 (versus 2–2.5) cm long. Type. Guyana • Upper Takutu-Upper Essequibo Region: Wassarai [Wassari] Mts., 0.5–1 km S of camp at base of highest peak, 01°33'N, 059°14'W, 275–400 m elev., 4 Sep 1999 (fl, fr), H. D. Clarke, R. Williams, & C. Perry 8189 (holotype: US [01317225]!; isotypes: BRG-n. v., GENT-n. v., TEX-n. v.). Description. Erect shrubs, to 1 m tall; stems densely stellate-pubescent. Leaves simple, entire, leaf blades broadly ovate, very faintly 3 - lobed, slightly asymmetrical in shape, decreasing in size towards the stem apex, 7–11 × 5–11 cm, bases cordate with a wide sinus, margin denticulate to subentire, teeth rounded (not sharp), apices acute to broadly acute, palmately 5–7 - nerved from the base, mid-rib and 2 ° veins prominent below, slightly raised above, densely stellate-pubescent below, heterotrichous with a bed of smaller stellate hairs overlain by larger stellate hairs, lamina not visible, sparsely stellate-pubescent to glabrate above, lamina visible; petioles 2.5–4 cm long, densely stellate-pubescent; stipules falcate, ca. 10 × 1 mm, densely pubescent, caducous. Inflorescences axillary, (2 –) 3 - flowered; peduncles 2–4.5 cm long, ± equal to or shorter than petioles in length, articulated ca. 2–3 mm below calyx. Floral buds globose, densely yellowish villous, sepals valvate. Involucel absent. Calyx campanulate, gamosepalous, 5 - lobed, ca. ½ or slightly more divided at anthesis, lobes broadly triangular, 1 × 0.6 cm, densely stellate-pubescent externally, stellate-pubescent internally near margin, nectariferous at base. Petals rotund, ca. 1.2 × 1.2 cm, claw short, ca. 2 mm long, yellow, external surface with minute, whitish, multicellular hairs, inner surface glabrous. Staminal column ca. 1.2 cm long, glabrous; filaments clustered apically, ca. 3 mm long. Styles slightly exceeding the anther mass in length. Stigmas capitate. Schizocarps exceeding the calyx, 1.5 × 2 cm, ± oblate, stellate-pubescent. Mericarps ca. 8, unilocular, 4 - seeded, rhomboid, ca. 1.2 × 0.8 cm, outer wall densely pubescent, inner wall sparsely stellate-pubescent, especially towards margin. Seeds teardrop-shaped, ca. 2–3 mm long, pubescent with short simple hairs, raphe ± glabrous. Etymology. The species epithet honours H. David Clarke who, while employed by the Biological Diversity of the Guiana Shield Program, National Museum of Natural History, Smithsonian Institution, was an adventurous and discerning plant collector in Guyana (see Kelloff et al. (2011)). Distribution. At present, known only from the Wassarai [Wassari] Mountains in southernmost Guyana near the Brazilian border (Kelloff et al. (2011): map 9, trip 18) where it was found in dense forest on red sandy clay. Discussion. This is the first record of Callianthe occurring in the Guianas. For convenience, C. clarkei was compared to C. sylvatica, but I am reluctant to consider the two species closely related. Their inflorescences and flower petals are quite different. In fact, the inflorescence of C. clarkei resembles that of several collections from Putumayo, Colombia that are associated here with C. sylvatica with doubt (see below).