The genus Callitriche (Plantaginaceae: Callitricheae) in South America Author Lansdown, Richard V. 0000-0003-0984-4552 Ardeola Environmental Services, 45 The Bridle, Stroud, Gloucestershire, GL 5 4 SQ, United Kingdom & Honorary Research Associate, Royal Botanic Gardens, Kew, Richmond, Surrey, TW 9 3 AE, United Kingdom & r. lansdown @ kew. org; https: // orcid. org / 0000 - 0003 - 0984 - 4552 r.lansdown@kew.org Author Hassemer, Gustavo 0000-0003-4365-6934 Câmpus de Três Lagoas, Universidade Federal do Mato Grosso do Sul, CEP 79613 - 000, Três Lagoas, MS, Brazil & g. hassemer @ ufms. br; https: // orcid. org / 0000 - 0003 - 4365 - 6934 g.hassemer@ufms.br text Phytotaxa 2021 2021-05-19 501 1 85 118 http://dx.doi.org/10.11646/phytotaxa.501.1.3 journal article 10.11646/phytotaxa.501.1.3 1179-3163 5424744 9. Callitriche hegelmaieriana Lansdown & Hassemer , sp. nov. Type: — VENEZUELA . PORTUGUESA : Wet places by road, selva nublada [cloud forest], 15 km al Este de Chabasquén , 67 km al NNO de Guanare , 9º 26–27’ N, 69º 54–55’ W, 1450–1520 m , 29–31 December 1982 , J.A. Steyermark et al. 126665 ( holotype NY!) . Diagnosis: — Callitriche hegelmaieriana can be distinguished from all other Callitriche species by the combination of ♀ and ♂ flowers in most aXils, fruit < 1 mm high and highlY compleX leaf venation. Description: —Stem and leaf scales present. Leaf bases connate. Linear leaves unknown, expanded submerged or floating leaves unknown, apical leaves not forming a floating rosette, leaves of terrestrial plants 6.9–10.0 × 2.7–4.8 mm , petiole 1.9–3.3 mm long, venation complex, both within and outside secondary veins. Bracts apparently lacking. GenerallY ♀ and ♂ flowers in both of a pair of aXils. StYle erect, persistent ≤ 0.2 mm long. Filament ≤ 0.6 mm long; anthers 4 mm wide; pollen yellow. Fruit on pedicels 0.3–0.5 mm long, slightly wider than high, dark brown when mature, 0.7–0.8 × 0.8–1.0 mm, broadly winged throughout, strumose. Illustrations: — Figure 1 (j). Distribution: — Callitriche hegelmaieriana is known only from two collections from Venezuela .Known altitudinal range: 1450–1800 m . Etymology: —The specific epithet commemorates the German botanist Christoph Friedrich Hegelmaier (1833– 1906), who greatly contributed to taxonomic knowledge of Callitriche . Notes: — Callitriche hegelmaieriana is a very unusual species, showing characteristics of terrestrial taxa, such as the ♀ and ♂ flowers in most aXils and lack of bracts, but contrasting with the leaves which are variable in size and have extremely complex venation which is more typical of amphibious taxa. Collection of more specimens may show that C. hegelmaieriana is capable of developing floating or submerged forms and that the two known specimens simply represent terrestrial forms of this taxon. It is very close to C. turfosa , from which it differs in the very complex leaf venation, broader wing to the fruit, shorter style and shorter filament. Conservation status: —Available information is inadequate to derive an informed assessment of the conservation status of C. hegelmaieriana and it is therefore classed as Data Deficient (DD). Additional material studied ( paratypes ): — VENEZUELA . LARA : In open places on soil, sieve nublada, entre le Encrucijada y el camino al Parque Nacional Yacambú de El Blanquito , 10–15 km SSE de Sanare , Estado Lara , 1750–1800 m , 7 August 1970 , A. Steyermark et al. 103550 ( US ) .