Strobilanthes sunhangii (Acanthaceae), a new species from Tibet, China

Abstract A new species of Acanthaceae, Strobilanthes sunhangii, is described from Mêdog County, Tibet, China. Morphologically, the new species is closely similar to S. medogensis and S. divaricata, but S. sunhangii differs in having glabrous stems, longer spikes, glabrous rachis, double curved corolla and glabrous calyx, different stamens and style.


Discussion
Morphologically, the new species is closely related to Strobilanthes medogensis in having similar leaves and slender spikes, but differs in having glabrous stems, longer spikes, glabrous rachis, double curved corolla and glabrous calyx, different stamens and style (Li 1985;Wood 1994;Hu and Tsui 2002;Deng et al. 2006;Hu et al. 2011). In addition, the new species is also related to S. divaricata in the glabrous stems and calyx, slender spikes, but differs in having longer spikes, double curved corolla, different stamens and style (Wood 2001;Adhikari 2018). The new species is quite different from all other known species in its unique corolla shape. The corolla of S. sunhangii are bent twice, at the base and middle of throat, respectively, while that of other species is  Table 1.
Till now, no infrageneric classification has been established. Bremekamp (1944) divided the subtribe Strobilanthinae into 54 genera and 27 informal groups. However, his classification is not supported by the studies of the only molecular phylogeny of Strobilanthes (Moylan et al. 2004) and morphological analysis (Carine and Scotland 2002). In this study, S. divaricata and S. medogensis, two species closest to the new species, were not included. Bremekamp placed S. divaricata into his new genus Diflugossa Bremek., which is characterised by the single flowers on each node on rachis, arranged in an open panicle, bracts small, deciduous and corolla straight. However, S. divaricata is quite different from other species of Diflugossa, which was informally placed in Panicle groups by Wood and Scotland (2003), in its paired flower on the rachis, arranged in spikes. S. medogensis was placed in Goldfussia Nees, which is characterised by the flowers arranged in congested head-like spikes and then compounded into small panicles, stamens 2-paired, the shorter pair unequal, nodding, anthers spherical (Li 1985). Obviously, Stems often zigzag above, angular, glabrous.

Corolla colour
Corolla outside and lobes pinkishwhite, inside purplish-pink.
Corolla yellowish-white but dull purple on lobes.

Corolla
Corolla 2.8-3.3 cm long, tube basally cylindrical and ca. 3 mm wide by ca. 6 mm long, then bent to ca. 90° and gradually widened to 9-12 mm wide at middle by 16-18 mm long, then second bent to ca. 90° and tube upper cylindrical and 9-12 mm wide by 16-18 mm long.
Corolla ca. 2.5 cm long, straight, tube basally cylindrical and ca. 2 mm wide by ca. 1 cm long, then gradually widened to 1-1.5 cm at mouth.
Corolla 3-3.5 cm long, tube cylindrical at base for 1 cm, then gradually widened up to 0.8 cm at mouth, straight or slightly bent towards mouth.

Corolla lobes
Corolla lobes widely elliptic, ca. 8-9 × 7-8 mm, apices emarginate. these three species form a species complex and further studies on the placement in the genus are necessary, depending on the establishment the infrageneric classification. Pollen morphology has been widely used in species delimitation of Strobilanthes (Chen et al. 2019), so we observed and measured the pollen grains of this new species. Pollens grains of the new species are prolate, 74.1 (72.2-76.1) × 49.7 (48.1-50.4) μm, P/E = 1.49, 3-colporate, 12-pseudocolpate, with reticulate exine. The detailed pollen grains morphology is provided in Fig. 4. The pollen grains of S. medogensis (as S. campaniformis) were observed by Wood (1994) and those of S. divaricata have not yet been observed. Both S. sunhangii and S. medogensis belong to type 3 recognised by Hu et al. (2011). Therefore, the close relationship between S. sunhangii and S. medogensis is also supported by the pollen morphology.
This species was observed by the authors during the Mêdog expedition in 2018. To date, we only collected flowering specimens and whether this new species has a plietesial life history requires further explorations.