Stapletonia rigoense L.B. Singha, P. Niri & R. Devi, 2018

Singha, Lal Bihari, Niri, Pakpi & Devi, Raseshowri, 2018, Stapletonia rigoense (Poaceae), a new bamboo species bearing very long internodes from Arunachal Pradesh, India, Phytotaxa 350 (1), pp. 79-85 : 82

Stapletonia rigoense L.B. Singha, P. Niri & R. Devi , sp. nov. ( FIGURE 3–4 )

TYPE:— INDIA. Arunachal Pradesh: Near Rigo village, Aalo, restricted natural population located at 28009´44˝ N Latitude and 94046´33˝ E Longitude ; elevation c. 400–500m asl.; hilly terrain, moist and warm climate; Col. No. 001/LBS/2017 (leafy twig and culm sheath) Holotype: Assam!

Erect to semiscandent bamboo. Culm: Moderate in size, 9–15m tall, 3.5–4cm in diamter, 3–8mm thick wall. Internode: 45–160cm or more long, longest at the middle, shorter at base and apex, with scattered golden brown hairs extending up to 1cm below the nodes and white colored ring up to 2cm below the node. Node: moderately swollen, glabrous, turns glossy when dry. Branch: Many, of same length at each node above the middle of the culm. Branch bud: Cuspidate at apex. Leaf: 17.5–37.5cm long and 3.5–6cm width; lanceolate, subulately acuminate above, tip twisted bearing pointed needle-like structure of 7–20mm long; base oblique, glabrous on adaxial surface whereas, scabrous on abaxial surface, with a 4–7mm long petiole. Leaf margin: Minutely scabrous; main vein prominent with 9–12 pairs of secondary veins and 4–5 pairs of intermediate veins; transverse vein absent. Leaf sheath auricle: Absent; Ligule -short, entire. Culm sheath: Slowly deciduous, 22.5–31.8cm long and 16–20cm width, broad, thick, crustaceous and scabrous, covered with appressed golden brown hairs (ca. 1mm long) on abaxial, glabrous on adaxial surface, oblique at the apex, margin ciliate with 2mm long golden brown hairs. Blade: Imperfect, erect, 15.5–27cm long and 12–14cm broad, triangular, striate with transverse veins, base not rounded but of similar size, inflated up to 5mm with reticulate veins; Margins: Ciliate, with white vertical bristles on lower half; triangular projection present at the base of the blade. Ligule: Narrow 1mm long, arching, dentate. Auricle: absent. Inflorescence: Not known.

Discussion:— TABLE1 shows the comparative morphological features of Stapletonia rigoense with the two species considered to be morphologically the most similar. S. rigoense resembles S. arunachalensis and S. seshagirianum in bearing narrow culms with long internodes and broad culm sheath blades with inflated base. However, the new taxon differs from the two in its twisted leaf apices bearing 7–18mm long pointed needle-like structure; erect culm sheath blade bearing a triangular projection at the base with dentate ligule. Presence of 10mm width ring of golden brown hairs below the nodes followed by 10mm width white-colored ring are also unique character for this species, whereas, in case of S. seshagirianum and S. arunachalensis , they lack such features on leaf and blade and bear only a white ring with white hairs below the nodes. On the other hand, S. seshagirianum bears linear-lanceolate narrow leaves and S. arunachalensis bears oblong-lanceolate leaves, whereas the leaves of S. rigoense are linear-oblong and the size is intermediate between the other two species. The rhizome of this species is clearly pachymorph and short-necked. The rhizome neck of S. arunachalensis was reported as extended ( Singh et al. 2009), and this was given as a generic character, but the length was not clarified and the illustration given did not demonstrate it very well. Possession of fringed leaf sheath auricles was also given as a generic character, but the occurrence of auricles is itself highly variable between congeneric bamboo species. Although the genus was thus distinguished mainly on its very distinctive flowering and fruit characters, and the inflorescence and fruit of S. rigoense are not known, it would nevertheless appear most likely that this new species should also be placed in Stapletonia . Much further work is required to describe the in-depth characteristics of several similar species in N E India and Burma, and to determine their generic affinities, morphological species boundaries and geographical distribution.

Etymology:— The species was collected from the forests near Rigo village of Arunachal Pradesh, India, hence the species has been named after its type locality.

Conservation status:— S. rigoense is known only from this recent collection in a small, restricted natural population. It is therefore assumed to be threatened.

Figures

FIGURE 3. A, An internode, B, tightly wrapped culm sheath and blade with inflated base, C, brown hairs with white rings below internode, D, triangular projection at the base of blade, E, dentate ligule on the culm sheath of Stapletonia rigoense.

FIGURE 4. A, Branch bud with cuspidate apex, B, culm sheath with blade, C, a leafy twig, D, twisted leaf apex with 7–18mm long needlelike structure, E, short-necked pachymorph rhizome of Stapletonia rigoense.