Checklist of aroids (Alismatales, Araceae) from Sabah (Malaysian Borneo) Author Wong, Sin Yeng Author Joling, Jyloerica text Check List 2021 2021-06-17 17 3 931 974 http://dx.doi.org/10.15560/17.3.931 journal article 10.15560/17.3.931 1809-127X Bucephalandra danumensis S.Y.Wong, P.C.Boyce & Kartini Figure 3G Material examined. MALAYSIA – Tawau • Lahad Datu , Danum Valley near second waterfall; 04°57′30″N , 117°41′47″E ; 21 January 1991 ; A. Bahaman et al. SAN 134426 ( SAN ) • Lahad Datu , Danum Valley Conservation Area , Kawag , Ali Baba Trail , Ali Baba Falls ; 05°02′42″N , 117°58′ 51″E ; 119 m elev.; 8 July 2018 ; Wong Sin Yeng, P. C . Boyce & Kartini Saibeh ( SAR ) . Identification. Bucephalandra danumensis is differenti- ated from all other Bucephalandra species with echinate/ papillate spadix appendix staminodes by the combination of the appendix and staminate flower zone being of about equal length, by the ellipsoid thecae separated by a deep sinus on the ventral surface, needle-like thecae extensions that curve upwards and interstice staminodes with conspicuously thickened, recurved margins. In appearance plants of B. danumensis most closely resemble those of B. yengiae P.C.Boyce from Kalimantan Timur , and an imperfectly known undescribed species from Kalimantan Utara ; B. danumensis differs from both by the equal proportions of the appendix and staminate flower zones (vs. appendix appreciably longer than staminate flower zone), and by the thick recurved mar- gins of the interstice staminodes (vs. staminode margins not or scarcely thickened, and not recurved). Bucephalandra danumensis differs from the only other Bucephalandra species from Sabah , B. ultramafica S.Y.Wong & P.C.Boyce , by the echinate/papillate appendix staminodes (vs. polygonal with very rounded angles, somewhat umbonate) and by not being obligated to ultramafic (ultrabasic) rocks ( Wong et al. 2018 ). Distribution and ecology. Endemic to Sabah . Known only from two localities, approximately 20 km distant, in the Danum Valley Conservation Area. Restricted to igneous stream beds and waterfalls outcropping through Cretaceous deepwater sediments in lowland perhumid forest between elevations of 120 and 310 m .