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 16. Callitriche praetermissa Lansdown & Hassemer , sp. nov. Type: — CHILE . MAGALLANES : In a tarn, near Hotel Rio Rubens (about 50 km SE of Natales ), 18 January 1941 , R. Santesson 1637 ( holotype NY!) . Diagnosis: — Callitriche praetermissa can be distinguished from all other Callitriche species by the combination of unwinged fruit ≥ 1 mm in diameter and widest in the middle, persistent bracts, long filament (≤ 4 mm long) and ♂ and ♀ flowers in each aXil or in one, opposed bY a solitarY flower. Description: —Stem and leaf scales present. Leaf bases connate. Lingulate leaves parallel-sided, 9.6–13.2 × 0.5– 1.1 mm , expanded submerged or floating leaves narrowly elliptic, 5.6–8.0 × 1.7–2.4 mm , petiole 1.8–4.3 mm long, venation usually simple but occasionally short branches arise outside the secondary veins and extend either toward or awaY from the apeX, apical leaves forming a floating rosette, leaves of terrestrial plants unknown. TYpicallY a ♀ and ♂ flower in one aXil, opposed bY a single ♀ flower. Bracts persistent, 0.5–1.7 mm long. StYles caducous, ≤ 1.0 mm long. Filaments ≤ 4.1 mm ; anthers 0.2–0.3 mm diameter; pollen Yellow. Fruit not strumose, subsessile, ± isodiametric, brown when mature, 1.0–1.1 × 1.0– 1.2 mm , unwinged. Illustrations: — Figure 5 (e). Distribution: — Callitriche praetermissa is known only from the type specimen which was collected from a tarn near Magallanes , Chile in 1941. Etymology: —The specific epithet means “overlooked” or “neglected” because this is not a striking species and has been overlooked by other botanists. Notes: — Callitriche praetermissa is known only from the type gathering, it is not a particularly striking species and in a genus which is extremely under-collected it is not surprising that it has been overlooked. There is a need to re-visit the type locality to establish whether it still occurs and to survey potentially suitable habitat in the region to attempt to find other populations. Conservation status: —Available information is inadequate to derive an informed assessment of the conservation status of Callitriche praetermissa and it is therefore classed as Data Deficient (DD).