Justiciathailandica, a new species of Acanthaceae from Thailand

Abstract A new species of Justicia (Acanthaceae), J.thailandica, is described and illustrated from Thailand. The new species belongs to Justiciasect.Harnieria and is similar to J.quadrifaria and J.championii, but differs on account of the obviously densely white indumentum in the inflorescence bracts and calyx, ovate leaf blades with margin usually entire, spathulate inflorescence bracts and length ratio of calyx to mature capsule. It is assessed to be “Near threatened” (NE) according to IUCN Red List Category and Criteria. Pollen and seed morphology characters are also reported. Species of Justiciasect.Harnieria in Thailand are discussed and a key to the three recognized species is presented.


Introduction
Justicia L. is the largest genus in the family Acanthaceae and consists of about 600 species distributed in tropical and temperate (to a lesser extent) regions of the world (Graham 1988;Hu et al. 2011;Mabberley 2017). It is characterized by the tubular and bilabiate corolla with stylar furrow (rugula) in the upper lip, two stamens usually with the lower anther-theca spurred at base, "Knötchenpollen'' pollen grains, and 4-(rarely 2-)seeded stalked capsules (Lindau 1894;Graham 1988;Hu et al. 2011). The recent molecular evidence Kiel et al. 2017) indicated that the genus Justicia in the broad sense is polyphyletic and might be further separated into several independent genera. At the moment, we follow the treatment of Graham (1988) who divided the genus into sixteen sections.
Sect. Harnieria (Solms-Laubach) Benth. is characterized by the abbreviated axillary spikes, leaf-like inflorescence bracts, fusiform capsules and tuberculate seeds (Tong et al. 2016). It comprises approximately 76 species distributed in the tropical and subtropical regions of Africa and Asia with two species extending to Australia (Barker 1986;Hedrén 1989;Tong et al. 2016).
In the course of revising Justicia sect. Harnieria from Asia, some specimens collected from Thailand and identified in herbaria as J. quadrifaria (Nees) T. Anderson or J. championii T. Anderson appear to represent an undescribed species, which differs from the latter two species by the characters of indumentum, leaves, petiole, calyx, inflorescence bracts and length ratio of calyx to mature capsule.

Materials and methods
The morphological comparison with related species in Justicia sect. Harnieria was based on studies of herbarium specimens and information gathered from literature. Pollen grains and seeds were taken from dried specimens (Beusekom et al. 3759, MO2366671) and mounted on aluminium stubs coated with gold in a sputter coater after being cleaned in water using ultrasound, and then examined using scanning electron microcopy (SEM; JSM-6360LV). The polar (P) axis and equatorial (E) diameter were measured by imaging analyzer (Smile View 2.1; JEOL Tokyo, Japan). Pollen terminology follows Erdtman (1969) and Punt et al. (2007). Seed terminology follows Hedrén (1989) and Rueangsawang et al. (2012).  blade ovate (not oval, oblong to rarely ovate) with margin usually entire (not slightly undulate), apex shortly caudate or acute (not acuminate), base cuneate (not decurrent), petiole 8−12 mm (not 5−7 mm) long, calyx densely white villous (not pubescent), inflorescence bracts spathulate and villous (not ovate to obovate and sparsely pubescent) and capsule longer than the calyx (not shorter than the calyx). It is also similar to J. championii, but differs by the whole plant being white villous (not pubescent), and inflorescence bracts spathulate and villous (not obovate-spatulate with apex emarginate and sparsely pubescent).
Etymology. The specific epithet "thailandica" is derived from Thailand, where the new species is found.
Phenology. The new species was recorded in flowering from August to November and fruiting from October to December.
Distribution and habitat. Justicia thailandica is only known from Thailand (Fig.  4). It grows in the thickets on the limestone hills or evergreen forest at elevations of 400−900 m.
Conservation status. Currently, Justicia thailandica is only known from seven locations of Thailand with eight collections and the estimated extent of occurrence more than 20000 km 2 . We speculate that it may be widespread in Thailand, but is likely to qualify for a threatened category in the near future due to its vulnerable karst habitat and human activities leading to a decline in such habitats. It is therefore assessed as "Near threatened" (NE) according to the IUCN Red List categories and criteria (IUCN 2017).
Justicia championii was first recorded in Thailand by Rueangsawang (2012) based on specimens (e.g. Wongprasert et al. 30402,. However, J. championii, is currently known only from China and N Vietnam according to our worldwide specimen examination and is very similar to J. quadrifaria, but differs by the leaf shape and may be merged with the latter. After detailed comparison between the type specimen of J. championii and some Thai specimens (e.g. van Beusekom et al. 3759,Koyama et al. 30402,van Beusekom et al. 3362) identified in herbaria as J. championii or J. quadrifaria, we found they are obviously different and represent the new species described above. The clearest difference between J. thailandica and J. championii is that the calyx is densely white villous in J. thailandica (not pubescent) and inflorescence bracts are spathulate and villous in J. thailandica (not obovate with apex emarginate and sparsely pubescent). The leaves also tend to be different with the leaf blade ovate and white villous in J. thailandica (not lanceolate, oblong to oval and pubescent) with margin usually entire (not slightly undulate), apex shortly caudate or acute (not obtuse), base cuneate (not decurrent), (Fig. 5; Tab. 1). However, these leaf differences represent trends in a spectrum of variation rather than clear discontinuities.
Morphologically, Justicia thailandica is also similar to J. quadrifaria, but it can be easily distinguished from J. quadrifaria by the leaf blade being ovate and white villous (not oval, oblong to rarely ovate and pubescent), margin entire (not slightly undulate), petiole 8−12 mm (not 5−7 mm) long, apex shortly caudate or acute (not acuminate), base cuneate (not decurrent onto the petiole), calyx densely white villous (not pubescent), inflorescence bract spathulate and villous (not ovate to obovate and sparsely pubescent) and mature capsule longer than the calyx (not shorter than the calyx).
Justicia quadrifaria was recognized to be widely distributed in the tropical region of S to SE Asia from India, Indochina to Malay Archipelago and South China (Ridley (1923; Hu et al. 2011). However, it is restricted to NE India and Bangladesh based on our worldwide specimen examination. J. zollingeriana (Nees) C. B. Clarke was reduced to J. quadrifaria or Calophnodes quadrifaria by some authors (Clarke 1907;Ridley 1923, Hu et al. 2011). However, it can be easily distinguished from the latter by the plant being glabrous (not pubescent in J. quadrifaria), calyx 4-5 mm (not 7-7.3 mm), capsule obviously more than 1.5 times longer than the calyx (not shorter than or subequal to the calyx) and leaves in each pair obviously unequal in size (not equal or subequal). J. zollingeriana is distributed in SE Asia from Thai Peninsular to Malay Archipelago. In Thailand, the species was first recorded as a synonym of J. quadrifaria by Hosseus (1908) based on specimen "Hosseus et al. 228", and then some specimen (e.g. Kerr 7375, Garrett 316) of the species were reported under J. quadrifaria by Imlay (1938), while some specimen (Marcan 1528 and Lakshnakara 772) were under J. quadrifaria var. salicifolia by Imlay (1938).
In the course of revising Thailand species of sect. Harnieria, we have confirmed there are three species in Thailand, viz. J. zollingeriana (Nees) C. B. Clarke, J. multinodis R. Benoist and a new species, J. thailandica, described here.
A comparison of characters between Justicia thailandica, J. quadrifaria, J. championii and J. zollingeriana is provided in Table 1. An identification key to Thai species in sect. Harnieria is provided below.