A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
agamospermy. Intraspecific polyploidy has been
reported in Hopea odorata and Dipterocarpus
tuberculatus (Jong 1976).
It has been demonstrated that certain species produce
polyembryonic seeds (Maury 1968, 1970a, b, Kaur et
al. 1978). Shorea ovalis ssp. sericea is tetraploid with
frequent polyembryony. These polyembryos originate
from nucellar cells at the micropilar end of the ovule
(Jong and Kaur 1979). However, fruit formation in S.
ovalis requires stimulation of pollination (Chan 1980),
which is pseudogamous. Pollen tubes have been observed
in some embryological preparations, thus the possibility
exists that a zygotic embryo is sometimes formed. Some
participation by embryo-sac cells other than the egg in
the formation of pro-embryos, in addition to those
derived from the nucellus (Jong and Kaur 1979), could
also be possible.
On the basis of chromosome number (odd
polyploidy) and other tentative evidence, it may be
inferred that all triploids or near triploids (Kaur et al.
1978) may also be apomicts with polyembryony. The
triploid condition may have arisen in some cases from
hybridisation between diploid and tetraploid congeners.
Agamospermy may indeed provide a mechanism for
overcoming chromosome sterility, and/or for the
stabilisation of a heterozygous combination favoured by
natural selection (Grant 1971 in Jong and Kaur 1979).
A close association between agamospermy,
polyploidy and hybridity has been demonstrated in a wide
range of temperate angiosperms (Gustafsson 1947,
Stebbins 1960). Even though much available evidence is
indirect, such a pattern may also occur in Shorea and
Hopea.
Apomictic plants are troublesome for taxonomists
because of the multitude of biotypes or microspecies
that result from agamospermous reproduction; the
periodic occurrence of hybridisation involving
facultative apomicts and related sexual species generate
additional variant forms which add to the complexity of
the variation pattern. Some classificatory difficulties in
Dipterocarpaceae at the supraspecific level presented by
Shorea and Hopea may well be attributable to the
presence in each genus of species groups or agamic
complexes in which sexual and related agamospermous
taxa exist side by side. Agamospermy whether facultative
or obligate could well be an important contributory factor
to the floristic diversity of the lowland mixed dipterocarp
rain forests of southeast Asia (Kaur et al. 1978).
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Present Classifications
The four more recent classifications (Tables 1, 2, 8) of
the family Dipterocarpaceae (Ashton 1964, 1968, 1982,
Meijer 1963, 1979, Maury 1978, Maury-Lechon 1979a,
b, Maury-Lechon and Ponge 1979, Kostermans 1978,
1992) have retained large parts of the previous
classifications from Heim (1892) and Symington
(1943).
Meijer has only taken into consideration the genera
growing in Sabah and Kostermans has centered his works
on Sri Lankan taxa and the three non-Asian genera.
Ashton had a taxonomical approach, while Maury-
Lechon concentrated on the definition of natural groups
and their phylogenetic trends. They both utilised the
results of anatomy studies produced by Whitmore (1963)
on bark, Gottwald and Parameswaran (1964) and Brazier
(1979) on wood. Likewise, they used works on cytology
from Jong and Kaur (1979), embryology,
chemotaxonomy (Ourisson et al. 1965, Diaz and
Ourisson 1966, Diaz et al. 1966, Ourisson 1979) and
Main aspects of Ashton’s classification (see also
Tables 1, 2, 8)
Taxonomical levels
Family (1): Dipterocarpaceae (16 genera, 3
sub-families, 2 tribes)
Sub-families (3): Pakaraimoideae: 1 monospecific
genus, 2 sub-species
Monotoideae: 2 genera Monotes
(more than 24 species),
Marquesia (about 3 species)
Dipterocarpoideae (2 tribes, 13
genera, 17 sections, 12 subsections):
Tribes (2): Dipterocarpi (8 genera, 4-5
sections): Dipterocarpus,
Anisoptera (2 sections), Upuna,
Cotylelobium, Vatica (2-3
sections), Stemonoporus,
Vateria, Vateriopsis.
Shoreae (5 genera, 13 sections,
12 sub-sections): Hopea (2
sections, 4 subsections), Shorea
(11 sections, 8 subsections),
Parashorea, Neobalanocarpus,
Dryobalanops.