The rediscovery of Strobilanthes tubiflos (Acanthaceae) in north east India

The recently rediscovered Strobilanthes tubiflos (C.B.Clarke) J.R.I.Wood is fully described for the first time. A key and photographs are provided to enable identification of similar species found in north east India. The rediscovery of S. tubiflos is discussed in the context of the botanical exploration of the region and the implications for conservation.


Introduction
As understood here, Strobilanthes Blume consists of around 400 species, thus making it the second largest genus in Acanthaceae (Mabberley 2017) after Justicia L. Historically there has long been uncertainty and disagreement about the limits of Strobilanthes with Nees (1832, 1847) and later Bremekamp (1944) dividing the Strobilanthinae sensu Bremekamp (1944) into many smaller genera whereas the opposite tendency was seen in publications by Anderson (1867), Clarke (1884), Terao (1983) and others. Our concept of the genus coincides with that of Terao (1983) who was the first to suggest that all species in the Strobilanthinae should be treated in a single genus. However, it is only since molecular studies have shown these segregate genera were nested within Strobilanthes (Moylan et al. 2003) that the broad concept of Strobilanthes has been generally accepted (Deng et al. 2006;Wood & Scotland 2009;Hu et al. 2011;Wood 2014;Deng 2019).
Despite its species richness, Strobilanthes is almost entirely restricted to tropical and subtropical Asia and is essentially a genus of hill forest enjoying a monsoon climate. In India, there are two centres of diversity: the central and southern parts of Peninsular India, from where about 65 species are recorded, and the Himalayas and hills of NE India with approximately 85 species. These two regions are separated by the Gangetic plain and have quite distinct Strobilanthes floras (Wood 1994: 202) with only one or two weedy species occurring in both regions. Species numbers rise rapidly along the Himalayan chain from west to east, one species is known from Afghanistan, 23 from Nepal, 30 from Bhutan (Wood 1994), but around 85 are found in the NE corner of India in the small eastern states of Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura (unpublished information).
Although the Khasi Hills of Meghalaya and the lowlands of Assam were relatively well-known to botanists in the 19 th century, other areas of this north eastern region were rarely visited and poorly known botanically throughout the 19 th and 20 th centuries. New plant records were associated with major expeditions, such as those recorded by Burkill in the Abor Hills in 1911, or with adventurous botanists and plant hunters, such as William Griffith and Frank Kingdon Ward. A large number of the species collected in the 19 th and early 20 th century were not recollected for many years after the end of the colonial era. However, in the last fifteen years almost all have been rediscovered and photographed by Indian botanists (Wood 2016), amongst whom the second author, Dipankar Borah has played an important role.
One of Griffith's discoveries in 1836 was Strobilanthes tubiflos, which was described as a variety of Strobilanthes petiolaris by Clarke (1884). It was subsequently collected by Kingdon Ward in March 1949 but there was no further evidence of its survival until it was rediscovered by Dipankar Borah and Momang Taram in February 2020. As this is a species that has never been fully described or illustrated, a full description is provided below together with photographs and information on its habitat and conservation status.
Further populations of Strobilanthes tubiflos may be found in this poorly known region, where other branches of the Brahmaputra River, such as the Dibang, emerge from the mountains, so this species should be classified provisionally as Data Deficient within IUCN (2012). It may well prove to be vulnerable (VUL) as suggested by Wood et al. (2003) because of the small number of populations, but there is insufficient evidence for a firm categorisation at the present time. NOTES. Strobilanthes tubiflos was originally described under the name S. petiolaris var. tubiflos C. B.Clarke (1884) and belongs to a group of species placed by Bremekamp (1944) in a separate genus, Sympagis (Nees) Bremek. Strobilanthes tubiflos is perhaps closest to S. kachinensis J. R.I.Wood & J.R.Benn. from Myanmar which also has only two fertile stamens but differs in the shorter obovate-spathulate, rounded to emarginate floral bracts 5 -6 × 3 -3.5 mm (not oblong, acute 6 -12 × 3.5 mm) and globose, rather than ellipsoid pollen. The bracts of the two species are illustrated and compared in Wood et al. 2003al. : 169. Wood et al. (2003 discussed the Sympagis group and listed the nine species that occur in NE India (Wood et al.   Nees, S. khasyana (Nees) T.Anderson (Fig. 2G), S. maculata (Wall.) Nees (Fig. 2B), S. monadelpha Nees ( Fig. 2A) and S. tubiflos (C.B.Clarke) J.R.I.Wood (Fig. 1). The group is characterised by its spicate inflorescence with imbricate, bracteate flowers and subglobose, triporate pollen usually lacking pseudocolpi, although S. tubiflos differs in shape from this typical pollen. The Indian species have 4-seeded capsules, the bracts are small and persistent and the calyx subequally 5-lobed. These species can be separated by the following key: Key to the species of the Sympagis group occuring in north east India