Herpetospermum operculatum ( Schizopeponeae , Cucurbitaceae ) , a new species from India , Myanmar and China

A new species of Herpetospermum (Schizopeponeae, Cucurbitaceae) is described from north-eastern India, northern Myanmar and southwest China (Xizang and Yunnan). Herpetospermum operculatum was previously confused with Herpetospermum (= Biswarea) tonglense, but differs primarily in having smooth yellow-striped fruit with operculum at stylar end, ascendent seed arrangement in fruit and prominent probracts and bracts. At least a part of the collections of Herpetospermum tonglense in Myanmar and China represent misidentification of this species.


INTRODUCTION
Of the two genera of the tribe Schizopeponeae Jeffrey adopted by Schaefer & Renner (2011a), Herpetospermum Wall.ex Benth.& Hook.f.s.l.(including unispecific Edgaria C.B.Clarke and Biswarea Cogn.) is a small genus with three species found among thickets and along riverbanks at altitudes of (1200 -) 1500-3000 m in the Himalayas, north-eastern India, Myanmar and south-western China.They are dioecious herbaceous climbers with solitary female flowers, male flowers in racemes, three stamens with conduplicate or straight anther thecae, pendent or horizontal ovules, and fibrous fusiform fruits dehiscing apically and longitudinally by three valves (Schaefer & Renner 2011b).Difference of opinion exists over the merger of these genera into one, as is evident from the recently published Flora of China (Lu et al. 2011) which considered them to be distinct.Clarke (1877), who described Edgaria and Warea C.B.Clarke (= Biswarea), acknowledged the overall resemblance of these taxa with respect to e.g., habitat, habit, proportion of male to female flowers, fruit size, shape and markings, and the resemblance has lead to frequent misidentifications (Chakravarty 1982).
While on survey and exploration tour to Sikkim and Nagaland for germplasm collection of cultivated cucurbits and their wild relatives during 2011 and 2012, the first and third author had come across a few wild plants superficially resembling Luffa Mill. in having an operculum at the fruit apex but strikingly different in flowers, internal fruit and seed morphology.While matching these plants with digital images in online herbaria of E, K, P and PE, we found that similar plants from Myanmar and Yunnan and Xizang provinces of China were kept under 'Biswarea sp.nov.' or 'Biswarea tonglensis' or 'Herpetospermum pedunculosum' at E, PE and PE/ K, respectively.Jeffrey recognized these as belonging to a new species under Biswarea (G.Forrest 9114 & T.T. Yu 16473) at E in 1981, but did not name them.The reason could be the scarcity of mature fruit and seed material, which provide reliable features for identification (Chakravarty 1959, Singh 1967) and also the difficulties involved in matching specimens with female flowers, male flowers and fruit (Jeffrey & Trujillo 1992).Differences among H. operculatum, H. tonglense, H. pedunculosum and H. darjeelingense are given in Table 1.
On describing the new species under Herpetospermum, there is a need to emend the generic description, as the present one (Schaefer & Renner 2011b) does not cover characters like 4-fid tendril, presence of probract, bracteate male racemes, 8 ovules per locule, ascendent arrangement of ovules, smooth (non angular/non ribbed) fruits and dehiscence through an apical operculum of the fruit.At the same time, we do not foresee any merit in elevating this to a new genus in the light of recent nomenclatural changes at generic level associated with these taxa as the result of molecular phylogenetic, seed coat and pollen studies (Kocyan et al. 2007, Schaefer & Renner 2011a).Also, while commenting on the controversy associated with the transfer of Luffa tuberosa Roxb. to Momordica by Cogniaux (1881: 454), Chakravarty (1959) in his revision of Cucurbitaceae of the Indian subcontinent, pointed out that the character 'operculum in fruit' need not be stressed upon as the generic distinguishing trait, in absence of other persuasive reasons.Therefore, the present species is described under Herpetospermum, which is the most convincing option at the present state of knowledge.Etymology.The species epithet refers to the lid-like structure (operculum) at the stylar end of the fruit, which is not found in other species of Herpetospermum.
Conservation assessment -The first author saw 12 plants in a single population spanning about 0.01 km 2 near the vicinity of Sadam village in South District of Sikkim; the populations are unlikely to face serious habitat loss.The third author saw only two female plants near jhum (shifting cultivation) area in Mesulumi village in Phek district of Nagaland; this may be indicative of probable threat to populations due to clearing of natural habitat.T.T. Yu in 1938 (Yu 16473) annotated that he had seen these plants commonly in Shunning (Yunnan).All other studied herbarium specimens (collected in 1912, 1982 and 2010) did not reveal anything about population size, abundance, threat, etc.Therefore, it is problematical to infer any trends from these scattered observations, although the fact that this conspicuous species did not attract the attention of taxonomists from three countries suggests a drastic population decline over decades.Considering also that this new species has been confused with two other species, we conclude that sufficient information is lacking to determine the threat status, and that the 'Data Deficient' (DD) category is most suitable, according to the criteria of IUCN (2001IUCN ( , 2013)).
Note -Clarke (1877) observed a higher proportion of male to female plants in the other three species of Herpetospermum under natural conditions.However, the first author has observed an equal proportion of male and female plants in this species in South District of Sikkim.Big yellow showy flowers in clusters call for further study of its potential as ornamental.Forrest 9114 (E) recorded flower colour as bright orange; this corresponds to the observation by the first author that just before anthesis, the flower is orangish, and later turns yellow.Sheng & Cheng 1431 (PE), from Medog County in Xizang, has fruits clearly showing an operculum mark.This specimen and Yu 16473 (E) have a mixture of both male and female flowers on the same herbarium collection.Borosova, Guo, Landrein, Liu, Osborne & Zhang 2046 [10CS 2046] (K) mentioned that seeds are creamy, probably due to observations at immature stage of fruit.Fully mature seeds are (grey-)black in colour.The line diagram of Biswarea tonglensis in vol.6 of Flora Yunnanica (Wu et al. 1995: 343) belongs to this species.The description in Flora of China (Lu et al. 2011: 33) for the above species with respect to length of bracts (2-3 mm), calyx segments (sometimes up to 20 mm) and pedicel of female flower (25-30 mm) indicates the likely overlap of character states of the new species with that of H. tonglense.However, we cannot exclude the possibility that true H. tonglense occurs in these countries.This new species is expected to occur in Bhutan and Indian states of Arunachal Pradesh and West Bengal (Darjeeling), and adjoining areas of Nepal.

Fig. 2
Fig. 2 Herpetospermum operculatum K.Pradheep, A.Pandey, K.C.Bhatt & E.R.Nayar.a. Habit; b. co-axillary male flower and male inflorescence (bud stage); c. close up of female flower showing stigma and petal with green acuminate tip; d. ovary after anthesis (note the probract at the axil); e. longitudinal and cross section of immature fruit showing ascendent arrangement of seeds; f. fruits with marked operculum, the third one from left shows the dehiscence through operculum; g. dry fruits showing horizontally well-knitted fibre, operculum and muricate seeds (a -e: K. Pradheep 1449 (type); f, g: K.C. Bhatt 1047).-Scale bars = 4 cm.
with subulate sepals almost equal to the length of about-to-open flower bud; seeds ± round with irregular erose margin and subrostrate proximal end, and with prominent projections/markings on either side.Type.K. Pradheep 1449 (holo CAL; iso DD, NHCP), India, Sikkim,

Table 1
Morphological attributes that can assist in distinguishing H. operculatum from H. tonglense, H. pedunculosum and H. darjeelingense.
Map 1 Distribution of Herpetospermum operculatum based on studied specimens.