Colocasia kachinensis, a new species of Araceae from Myanmar

Abstract Colocasia kachinensis S.S. Zhou & J.T. Yin, is described and illustrated as a new species of Araceae from Kachin, Mynamar. The morphological characters are compared to those of other Colocasia species. Colocasia kachinensis is closely related to C. menglaensis J.T Yin, H. Li & Z.F. Xu, 2004, but differs from in having an erect stem, no stolons, smaller size, a different pattern of surface bristle distribution and male flowers 1–4-androus with stamens connate in truncate synandrium.


Introduction
Colocasia is a genus of about 20 species distributed in tropical and subtropical Asia (Li and Boyce 2010). Currently, two sections are recognised within the genus: sect. Colocasia and sect. Caulescentes (Mayo et al. 1997). This new species belongs to section Caulescentes Engl., characterised by an erect stem.
Including the species described here, four Colocasia species are known in Myanmar (Kress et al. 2003): C. affinis Schott, C. esculenta (L.) Schott, C. kachinensis and C. menglaensis J.T. Yin, H. Li & Z.F. Xu. Colocasia menglaensis was first found in the same habitat as C. kachinensis.
During an expedition to Kachin in April 2016, two populations of an unusual Colocasia were encountered growing along the roadside in the understorey of a mountain rain forest. For the next two years, the authors monitored the in-situ population, as well as plants established in ex-situ collection and meticulously examined and documented flowering episodes of the species. The unusual Colocasia sp. was compared with closely allied species and the gathered evidence revealed that the species was new to science. Diagnosis. The morphological characteristics of C. kachinensis are closely related to those of C. menglaensis but C. kachinensis differs in having an erect stem (see Fig. 3 Description. Terrestrial perennial herbs with an erect stem. Plant 54 cm high; erect stem 12 cm long, 3 cm in diam. Leaves 3-4; petiole cylindric, pale greenish, glossy, 32 cm long, 0.6 cm in diam., sheath 16 cm long, 6 cm in diam.; leaf blade oblongovate, peltate, 18 cm long, 12 cm wide, upper surface glossy green, lower surface greyish-white; primary lateral veins pinnate, 5 pairs, pale green on upper surface, white and raised on the lower surface. Inflorescences (1-)3(-4) emerging when the leaves unfold, 27 cm long; peduncle cylindrical, pale green, glossy, 17 cm long, 0.5 cm in diam. Spathe constricted in the lower third, lower convolute part (tube) pale green, farinose, 3.5 cm long, 1.5 cm in diam., nearly cylindrical; lamina oblong-lanceolate, erect during early blooming period, pale yellow, 6.5 cm long, 3 cm wide. Spadix 7 cm long, female zone 2.5 cm long, 0.8 cm in diam.; sterile zone between female and male zones, cylindrical, white, 0.8 cm long, 0.3 cm in diam.; male zone, white, 2 cm long, 0.6 cm in diam.; appendix white, long conical, wrinkled, 2 cm long, 0.4 cm in diam. Flowers unisexual, perigone absent. Male flower: 1-4-androus, stamens connate in truncate synandrium, thecae lateral, oblong-lineal, dehiscing by apical pore. Female flower: ovary ovoid to oblong, 1 mm long, unilocular; ovules many, 42-58, n = 2, fusiform, translucent; placentae 3-5, parietal; stylar region absent; stigma discoid-capitate; berry not seen.
Phenology. Flowering in March to April. Fruiting unknown. Distribution and habitat. C. kachinensis is so far known from a single population in Kachin State, northern Myanmar, where it grows in humid dense mountain rain for-

Discussion
Colocasia kachinensis is similar to C. menglaensis, described by Yin et al (2004), because they both have similar pubescent leaves. It differs from the latter by having (i) an erect stem (see Fig. 3), (ii) no stolons, (iii) smaller leaf and inflorescence and (iv) glossy petiole and peduncle.
Colocasia menglaensis and C. kachinenis, which were introduced from Myanmar, have been grown in a small yard of Xishuangbanna Tropical Botanical Garden, Yunnan China. We then collected leaves of two species for observation. The lower surface of the leaf blade, observed with a 100× magnification, also shows that C. kachinensis differs from C. menglaensis. The short bristles of the former are uniformly distributed on the abaxial surface of the leaf, while those of C. menglaensis are concentrated on the veins on the abaxial surface (see Fig. 3).
Colocasia kachinensis is also different from other species in this genus by having 1-4-androus male flowers, with stamens connate in truncate synandrium (see Figure 4). In the genus of Colocasia, one usually finds 3-6-androus male flowers, with stamens connate in ± truncate synandrium (Mayo et al. 1997). Further differences are listed in Table 1.