ADDITIONS TO “RUBIACEAE OF THAILAND. A PICTORIAL GUIDE TO INDIGENOUS AND CULTIVATED GENERA”
Indo-Chine 3: 263. 1923; Craib, Fl. Siam. 2: 126. 1932.— Psilobium capillare Kurz, J.Asiat. Soc. Bengal 41(2): 313. 1872.— Morindopsis laotica Pit.. in H.Lecomte, Fl. Indo-Chine 3: 264. 1923, synon. nov. Fig. 4.
Distribution.— NORTHEASTERN: Phetchabun, Udon Thani, Nong Khai, Nakhon Phanom; EASTERN: Ubon Ratchathani; SOUTHWESTERN: Ratchaburi, Kanchanaburi; SOUTHEASTERN: Chanthaburi, Trat.
Notes.— Based on field observations, the species is an obligate (“strict”) rheophyte (not known to van Steenis, 1981, 1987, and therefore not included in his survey of the rheophytes of the world). It invariably grows in cracks of rocks (limestone, sandstone, granite) along or in rivers and streams, or in sandbanks. It is associated with various other rheophytes (often Homonoia riparia, Euphorbiaceae, and Syzygium ripicola, Myrtaceae), but never seems to be as common and conspicuous as these habitually similar plants and normally does not form large populations. This undoubtedly is one of the reasons for our assumption that M. capillaris is much more widespread than the documented, scattered distribution suggests. Another is that collectors, not being aware of the diversity of rheophytes, have frequently neglected these often difficult-to-access habitats and overlooked the species. In this context, collectors are also urged to produce accurate and precise habitat notes; were one to rely on the existing, not uncommonly very vague field notes, one would never guess that M. capillaris is a strict rheophyte.
Apart from being one of the relatively few rubiaceous rheophytes, the genus is remarkable for several reasons: the plant’s vegetative lateral branches and inflorescence axes (peduncles) are almost always in a clearly supra-axillary position, i.e., arise some distance above a leaf axil (Fig. 4B, D, F). This, together with the long, filiform peduncles bearing very small flowering heads, is a very good character combination to recognize the genus. It was presumably the shape of the inflorescence that tempted the author of the genus to call it Morindopsis (meaning “resembling Morinda”). This is somewhat unfortunate because the resemblance to Morinda is only a very superficial one and the two genera are not at all closely allied.
Morindopsis is dioecious; male and female inflorescences do not appear to differ much in their extent (in contrast to other dioecious Rubiaceae where female inflorescences are often less extensive and fewer-flowered than male ones; see Puff et al. 2005:32 for details). Both male and female flowers are variable in size and shape (even within populations) so that a trend to somewhat larger female and smaller male flowers recognizable in other dioecious Rubiaceae is not obvious. The genus’/species’ fruits are apparently adapted to water dispersal: trials have shown that they float although they do not contain any obvious air-filled tissue; their fruit wall is thick and leathery, most likely a good protection against quick dissolution and disintegration in water.
Morindopsis is best considered a monotypic genus, because the second species formally recognized up to now, M. laotica, is indistinguishable from the variable M. capillaris. In Flore Ge´ne´rale del’Indo-Chine,where M. laotica was first described (Pitard, 1923: 263), the key separating this species and M. capillaris is highly misleading. It is based on characters of female plants, i.e. stigma characters and calyx lobe length in relation to ovary (“calyx tube”) length, although the original diagnosis of M. laotica was based on a male