Begonia buchtienii Irmsch.

Moonlight, Peter & Fuentes, Alfredo F., 2022, AN UPDATED CHECKLIST AND KEY TO THE SPECIES OF BOLIVIAN BEGONIA, INCLUDING ONE NEW SPECIES, Edinburgh Journal of Botany 79 (407), pp. 1-66 : 46-47

8.35. Begonia buchtienii Irmsch. , Bot. Jahrb. Syst. 74: 595 (1949).

– Type: Bolivia, [Cochabamba Department, Prov. Chapare ], Antahuacana , im Tal des Espiritu Santo, 160 km von Cochabamba enfernt, [17°4′S, 65°39′W], 750 m, vi 1909, O. Buchtien 2263 (lectotype US [ US00115264 ] designated here; isolectotypes B ex US [ B100467926 ], NY [2: NY03091040 , NY03091041 ]) ; ibid., vi 1909, O. Buchtien 4653 (syntype US [ US00222383 ]). D.C. Wasshausen et al. in P.M. JØrgensen et al. (eds), Cat. Bolivia, Monogr. Syst. Bot. Missouri Bot. Gard. 129: 384 (2013) .

Distribution. Endemic to Bolivia.

Notes. Begonia buchtienii is one of four Bolivian members of Begonia sect. Ruizopavonia with a sparse to dense indumentum on the stem. It can be distinguished with ease from Begonia bangii , which has persistent, asymmetrical and ovate to semicircular stipules, but the differences between B. buchtienii , B. leptostyla and B. varistyla Irmsch. are unclear. Irmscher distinguished both Begonia buchtienii and B. varistyla from B. bangii on the basis of stipule shape and their having four tepals in the pistillate flower. Begonia leptostyla was not distinguished against any similar species, so it is unclear how Irmscher believed it to be different. We cannot distinguish these species based on Irmscher’s descriptions or type specimens, and there are numerous specimens that represent intermediates between these descriptions. We consider it likely that these three names represent only one or two species.

Nomenclatural notes. Edgar Irmscher described Begonia buchtienii Irmsch. (1949: 595) from material of O. Buchtien 2263 and 4653 in Washington herbarium. We select the sheet of the former ( US 00115264) as the lectotype of Begonia buchtienii because there is a specimen including six staminate flowers and one leaf from this collection in Berlin ( B100467926 ). This sheet also has a line drawing by Irmscher of the lectotype in Washington, and writing indicating that Irmscher considered O. Buchtien 2263 as the type. Unfortunately, none of the known type material of Begonia buchtienii includes pistillate flowers or fruits, despite Irmscher providing a full description of the pistillate flowers. Further authors may decide to designate an epitype with pistillate flowers matching Irmscher’s description.

Identification notes. Distinguished as the only Bolivian Begonia with pinnate venation; a tomentose indument on its stem; deciduous, triangular stipules; a transversely cordate leaf base; and large (> 1 cm long) tepals on the staminate flower (but see Notes above).

Based on Irmscher’s description, Begonia buchtienii differs from B. leptostyla in its transversely cordate leaf base (vs rounded), and from B. varistyla in its elliptic stipules (vs oblong-ovate) and its c. 11 mm long staminate tepals (vs c. 7.5 mm long).