Iguanura namsabiensis Henderson, Mu Mu Aung & Armstrong, 2020

Henderson, Andrew, Aung, Mu Mu & Armstrong, Kate, 2020, A remarkable new Iguanura (Arecaceae, Arecoideae, Areceae) from northern Myanmar, Phytotaxa 446 (1), pp. 77-80 : 77

Iguanura namsabiensis Henderson, Mu Mu Aung & Armstrong sp. nov.

Type:— MYANMAR. Sagaing Region, Hkamti District, Homalin Township , just outside Htamanthi Wildlife Sanctuary , Nam Sa Bi Village Management Area, 25˚19’2.7”N 95˚21’52.2”E, 155 m, 25 September 2016, K. Armstrong, Thet Yu Nwe, Phyu Phyu Hnin, Kyaw Zin Aung, Win Zaw Myint, Lin Zaw, Han Sein Myint, Phoe La Pyae 1596 (holotype NY02654852 !, NY02654857 ! , isotypes E! , RAF! ).

Figs. 1 & 2.

Stems not recorded (whole plant 3 m tall). Leaves pinnate, number unknown; leaf sheaths closed, tubular, not splitting opposite the petiole, densely reddish-brown tomentose; ocreas well-developed, becoming fibrous and disintegrating; petiole 14.0 cm long; rachis 89.0 cm long, covered adaxially and abaxially with dense, reddish-brown hairs; number of pinnae not recorded; venation sigmoid, adaxial veins prominent, rectangular in cross-section, secondary veins densely reddish-brown tomentose abaxially; basal pinna (measured along distal margin) 22.5 cm long, 0.8 cm wide (measured at widest point); middle pinna 31.7 cm long, 4.3 cm wide; apical pinna 20.7 cm long, 8.0 cm wide. Inflorescences infrafoliar, branched to 1 order; prophyll and peduncular bract scars 0.7 cm apart; peduncles 2.2 cm long; rachis length not recorded; rachillae 9, 23.2 cm long, 2.3 mm diameter, glabrous or sparsely tomentose; triads sunken in shallow pits lacking a distal lip; flowers not recorded; fruits (immature) ovoid.

Distribution and habitat:— Known only from northern Myanmar in subtropical forest at 155 m elevation.

Discussion:— There appear to be three groups of species of Iguanura . One comprises about 13 species and occurs only in Borneo. It is characterized by its open leaf sheaths and mostly interfoliar inflorescences, leaves with parallel venation, and seeds with homogeneous endosperm (e.g., I. elegans Beccari (1886: 103)) . Most species in this group have lobed anthers and ridged fruits. The second group comprises between two and seven species and occurs in Peninsular Thailand, Peninsular Malaysia, Singapore, and Sumatra. Species have open leaf sheaths and interfoliar inflorescences, leaves with parallel venation, and seeds with ruminate endosperm (e.g., I. wallichiana (Martius) Beccari (1886: 100)) . The third group occurs in Peninsular Thailand, Peninsular Malaysia, and Singapore, but only rarely in Sumatra. It is characterized by its closed leaf sheaths with mostly infrafoliar inflorescences, pinnae with sigmoid venation, and seeds with homogeneous endosperm. The group comprises 10–12 species (e.g., I. bicornis Beccari (1889: 188) , I. polymorpha Beccari (1889: 189)) and this is the group to which I. namsabiensis appears to belong. Only a short section of the leaf sheath is present, but it is presumed to be closed opposite the petiole, and has a well-developed ocrea, as other species in the group. Within the group, I. namsabiensis is most similar to I. bicornis in its infrafoliar inflorescences, short peduncles, and flower pits with scarcely developed distal bracteoles, but differs in its fruits that are not lobed at the apex. Quantitatively, I. namsabiensis differs from I. bicornis in its longer rachis (89.0 cm versus 26.0–45.0 cm), longer pinnae (31.7 cm versus 12.8–19.7 cm), and longer rachillae (23.2 cm versus 7.0–11.0) cm.