A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
Consistent Criteria for Definition of Species and
Sub-species
Consistent criteria (Ashton 1979a) for definition of
species and sub-species were expressed for
Dipterocarpaceae as follows:
1. Size differences are not by themselves sufficient,
neither are differences of leaf size and shape combined.
Differences in fruit size are likewise unreliable
and rarely correlate with other characters; collections
from one tree in different years often exhibit
great variation. A consistent discontinuity in leaf
size, when correlated with differences in androecium
or gynoecium, in qualitative (not quantitative) characters
of indumentum, with qualitative characters of
the twig or stipule or with a discontinuity in the range
in the number of leaf nerves does constitute an adequate
criterion for separating species.
2. Subspecies can be defined where discontinuities occur
in the range of dimensions of parts, in tomentum
distribution and in density. However, sometimes taxa
which share a unique qualitative character, especially
of fruit or flower, are recognised as subspecies even
though they may differ qualitatively in vegetative
parts.
Experience has shown that this definition of
subspecies is sometimes too conservative (for example,
Shorea macroptera ssp. baillonii and ssp.
macropterifolia occur together in some forests, Vatica
oblongifolia ssp. multinervosa, ssp. crassilobata and
ssp. oblongifolia do seem at times to intergrade. This
definition of subspecies, albeit consistent, is essentially
arbitrary but may be useful when evidence of
hybridisation in nature is unavailable.
Ontogenetic Aspects of Morphological and
Anatomical Characters
In Dipterocarpaceae decisions on the primitiveness or
derived conditions of characters are drawn from personal
hypotheses on the evolutionary trends within and between
angiosperm families. Ontogenic trends may follow
evolutionary trends. Even in the absence of this
relationship, study of the embryonic trends helps to
understand taxonomic relations.
Chemotaxonomic studies have shown (Ourisson
1979) the existence of certain chemical directions for
molecular construction in the family: from the epoxyde
of squalene to the triterpenes of the resins, in all species
of dipterocarps sensu stricto.
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The embryogenesis from seed germination to young
seedling in dipterocarps analysed by Maury-Lechon has
demonstrated a unique direction for the construction of
the vascular structures in cotyledon node and petiole,
from simple to very complex (Maury 1978, Maury-
Lechon 1979a, b, Maury-Lechon and Ponge 1979). This
trend exists in certain species at different developmental
phases and morphological levels (node: base, mid-part,
top of petiole) within a single plant (e.g. Vateria
copallifera in Maury-Lechon 1979b; photographs Fig.
49). In other species the trend may be visible by
comparing plants of a given species (most genera of the
family: Dipterocarpus, Dryobalanops, Parashorea,
Vatica sections Vaticae and Pachynocarpus, Vateria,
Hopea and Shorea) or by comparison of different
species at a given stage of development and
morphological level as, for example, from the simple
trilacunar vascular structures of cotyledonary petiole in
Shorea curtisii, to the increasing complexity of
Stemonoporus affinis, S. reticulatus and finally the
trilacunar appearance of the very complex structure of
Vateria copallifera (Maury 1978, Maury-Lechon
1979b). Simplest structures (unilacunar with a single
resin canal in cotyledonary node) are remarkable in
Sunaptea, Cotylelobium, Upuna and also exist in certain
Hopea, Anthoshorea, Richetioides and Muticae.
Monotes and Marquesia have different (no canals and
different organisation of vascular bundles) and more
complex structures than the Asian simplest forms.
These simplest structures correspond to the taxa with
small winged fruits, well dispersed by wind, thus again
with the open areas and long distance migrations. These
structures allow a better putative relation with the African
and American taxa (simple but of different type and
devoid of resin canals). They could evoke ancestral
dipterocarp migrations in more open, windy and perhaps
drier environments than those of the present rain forest.
Polyploidy, Polyembryony, Apomixy and
Variability of Dipterocarp Characters
The two basic chromosome numbers tend to remain
constant within a single genus and between groups of
genera even in heterogeneous genera like Shorea and
Hopea. It is premature to say which of the numbers is
derived or ancestral (Jong and Kaur 1979). There is a
low frequency of polyploidy series and intraspecific
polyploids in the Asian genera Shorea and Hopea,
especially in cases where polyploidy is associated with