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 4. Callitriche ciliata Lansdown & Hassemer , sp. nov. Type: — ARGENTINA . SANTA CRUZ: Patagonia , 25 January 1932 , A. Donat s.n. ( holotype G barcode G00414940!) . Diagnosis: — Callitriche ciliata differs from all other Callitriche species apart from C. truncata subsp. fimbriata Schotsman (1967: 39) and some populations of C. truncata subsp. truncata in Morocco (RVL unpublished data) in the combination of stem and leaf scales lacking, flowers solitary, fruit winged and the wing degrading on maturity to leave exposed fibrillae on the margin. Callitriche ciliata differs from C. truncata subsp. fimbriata and Moroccan populations of subsp. truncata in its longer leaves and typically wider fruit. Distribution and morphological differences support the distinction from that species. Description: —Stem and leaf scales lacking. Leaf bases not connate. Lingulate leaves parallel-sided, 4–19 × 0.3–1.5 mm , expanded floating or submerged leaves unknown, apical leaves not forming a floating rosette, terrestrial leaves unknown. Flowers solitary. Bracts lacking. Style initially erect, eventually reflexed, appressed to side of ovary at base, sharplY recurved in apical half, ≤ 2.7 mm long. Filament straight, ≤ 0.6 mm long; anther reniform, 0.30–0.43 mm diameter; pollen colourless. Fruit not strumose, on pedicels ≤ 1 mm long, slightlY wider than long, greYish-brown when mature, 1.2–1.7 × 1.1–1.9 mm , wing 0.07–0.20 mm wide, initially entire, after ripening reduced to a fringe of the remains of the fibrils which are more or less simple or branched. Illustrations: — Figure 1 in Bacigalupo (1979b) (as C. truncata Gussone [1826: 4] ); Figure 1 (d–e). Distribution: — Callitriche ciliata is known from five specimens , two from Santa Cruz Province in Argentina , one from Bolivia and two from Peru . It seems likely that it is widespread in South America, probably occurring from Patagonia north along the Andes to Peru and maybe beyond, but is either scarce or under-recorded. Known altitudinal range: 3900–5000 m . Etymology: —The specific epithet means “ciliate”, a reference to the aspect the fruit wing acquires on fruit maturity. Notes: — Callitriche ciliata was recorded as C. truncata subsp. truncata by Bacigalupo (1979b) , but in most populations of the latter the wing of the fruit remains entire at maturity (apart from some populations in Morocco ). Callitriche ciliata is the only member of the C. hermaphroditica L. complex native to the Southern Hemisphere. The similarity to C. truncata subsp. fimbriata is striking but morphological differences are sufficient to justify its treatment as a separate species. Conservation status: —Available information is inadequate to derive an informed assessment of the conservation status of C. ciliata and it is therefore classed as Data Deficient (DD). Additional material studied ( paratypes ): — ARGENTINA . SANTA CRUZ : Hicken & Hauman ( Iter Patagonium ) 650 (SI). BOLIVIA . ORURO : Sajama , Carangas Province , Oruro Dept. , 13 May 1921 , E. Asplund 3979 (NY). PERU . Rio Blanco , 15000 ft. , 20–25 March 1923 , J.F. Macbride 3047 ( US ). CUZCO : Legamo , Alredidores de Yauri , Espinar Province , 3900 m ., 16 January 1961 , C. Vargas C. 13525 ( US ) .