The genus Trichosanthes L. (Cucurbitaceae) in Thailand ...

THE GENUS TRICHOSANTHES L. (CUCURBITACEAE) IN THAILAND (B.E.E. DUYFJES & K. PRUESAPAN) 77
goose’s egg. Some general morphology of Trichosanthes, with emphasis on characters
to be used in the determination of the species, is given below. With the treatment of the
species, specimens are only cited when few specimens for Thailand are known; for
other specimens one is referred to the identification list.
Subdivision of Trichosanthes
Trichosanthes, in subfamily Cucurbitoideae, is the largest genus in the family. It
has a wide genus concept and comprises more than 100 species in (sub)tropical Asia, to
the east as far as (sub)tropical Australia and the Pacific. Centres of species diversity are
China and Malesia. For Malesia, Rugayah & De Wilde (1999) and Rugayah (1999)
largely followed the subdivision of the genus as proposed by Jeffrey (1980) and some
Chinese authors (Yueh & Cheng, 1974) for China, based primarily on characters of the
male bracts, and the seeds. The 17 species in Thailand do not allow for original research
on the subdivision of the genus, but a survey of their characters made it clear that the
species cannot easily be placed in the sections as previously proposed by Yueh &
Cheng (1974), Huang et al. (1998) or Rugayah (1999). We are of the opinion that new
research comprising all species over the whole range of the genus is needed to arrive at
a satisfactory division.
Pruesapan & Van der Ham (in press) investigated pollen of some 40 species,
including those of Thailand, and found some resemblance with the existing
subdivisions.
CHARACTERS USED IN THE KEY TO THE SPECIES AND
IN THE DESCRIPTIONS OF THE SPECIES
Habit
The observation of living plants in the field is useful for the assessment of various
aspects of the habit of Trichosanthes because these aspects may be not clear from the
herbarium specimens. Most species are perennial climbers, often with tuberous roots,
and some are annual. Perennial female plants frequently die after fruiting
(monocarpous), but new shoots may be produced by the tubers in some species.
Sexual condition
Whether a species is monoecious or dioecious can be determined by the presence
of male flowers as well as female flowers or fruits on the same herbarium specimen, or
preferably by observing living plants. In other genera it may be variable but in
Trichosanthes most species are dioecious, and only some are monoecious, e.g.
T. cucumerina and possibly T. siamensis.