Heteranthera yucatana Carnevali, Tapia-Munoz & J. R. Grande 2022, sp. nov.

Heteranthera yucatana Carnevali, Tapia-Muñoz & J.R. Grande, sp. nov. Type:— Mexico. Yucatán: Municipio Dzemul, 2 km al S del entronque a las Ruinas de Xtampú (sic., Xcambó), approx. 21°18’00”N, 89°19’58”W, selva baja caducifolia con cactáceas columnares, 8 November 2000, G. Carnevali & J. L. Tapia 6262 (holotype, CICY!; isotypes, FLAS!, K!, MEXU!, MO!, SEL!, TEX!, UADY!, UJAT!, US!, VEN!). Figures 1, 2. A Heteranthera species similar to H. seubertiana but its leaves are pubescent (vs. glabrous) and the flowers are smaller (perianth lobes 3.2 mm vs. 7 mm), lilac with the base white-greenish (including an upper yellowish spot), whereas in H. seubertiana the petals are yellow and instead of the basal blotch there is a dark maroon-red spot at about 1/3 of the perianth lobes length. Herbs 4.5–11.5 cm tall(including the inflorescence),annual, hydrophytic in fresh or brackish water, partially submerged, emergent or paludal, growing at the margins of seasonal ponds or water-filled rock crevices. Roots delicate, diffuse, white and dark blue in dry specimens, not exceeding 8.0 cm long. Stems consisting of creeping, aquatic rhizomes and aerial +/- erect branches; rhizomes buried under the substrate, rooting throughout, reduced or up to 4.5 cm long, 1 mm diameter, with at least one node near the apex; branches 1–5 per plant, subtended by a hyaline prophyll with acute apex, basally truncate. internodes 0.6–1.2 cm long, glabrous. Leaves distichously-alternate, distributed along the stem, floating to emergent; leaves 3.3–9.0 × 0.3–0.6 cm, linear, sometimes wider near the apex, pubescent, pubescence mainly abaxial, consisting of more or less sparse glandular capitate hairs, ca. 0.2 mm long; sheath 0.9–1.6 × 0.3–0.6 mm, narrowly rectangular, with the apex appendiculate, basally truncate, marginally hyaline; ligule 2-parted, 2.0–3.0 mm long, with two different types of tissue, one of them like the rest of the sheath and blade, the other one hyaline like the prophyll; leaf blade 2.5–7.7 × 0.2–0.6 cm, linear, basally ...