A review of dipterocarps - Center for International Forestry Research

Biogeography and Evolutionary Systematics of Dipterocarpaceae
dipterocarpol) is considered of inferior rank (generic:
for example, the hydroxydammarenon in genus
Dipterocarpus; sub-generic: the sesquiterpenes derived
from humulene at infrageneric rank).
From the study of pollen, fruit, embryo and young
seedlings (Maury 1978, Maury-Lechon 1979a, b)
biological characters of seed germination have been used
together with pollen types and exine structure, at familial
and sub-familial levels. Other characters of the anatomy
of very young seedlings and the morphology of ripe fruit,
the epidermis of seedling cotyledons and the two first
leaves, have been hierarchically ordered. Thus a new
classification was proposed, without formal descriptions,
to serve as a base for further studies on the delimitation
of natural groups of taxa inside Dipterocarpaceae sensu
lato (cf. below: present classifications).
Supraspecific Taxa in Dipterocarpaceae
Apart from the above familial and sub-familial rank, four
principal taxonomic criteria have been expressed (Ashton
1979c) for definition of supraspecific taxa in current
revisions: 1) at least a pair of characters which are not
functionally interrelated; 2) these characters should be
common to all species in the taxon; 3) there should
therefore be clear discontinuities in the variation
between taxa; and 4) the prime goal of taxonomy should
be to achieve nomenclatural stability. ‘Given these
criteria, genera must be regarded as essentially artificial
groupings in the sense that they are defined by breaks in
the total range of variation’ (Ashton 1979b, p. 129).
In Asian Dipterocarpaceae most characters
correspond to two main trends expressed in the tribes
Dipterocarpi and Shoreae sensu Ashton (1979b), which
are nearly equivalent to ‘Valvate’ and ‘Imbricate’ groups
sensu Maury-Lechon (1979a) except the Dryobalanops
genus, which in the latter is intermediary (certain
characters of Imbricate type and others of Valvate type).
In these groups the characters are greatly or weakly
predominant but their presence (and intensity) is not
systematic in all species of the group. This situation
explains the difficulty of establishing clear deliminations
or affinities. Chromosome numbers (n=7 in most
Imbricate species and n=11 in Valvate taxa) illustrate
these facts and provide some explanation.
The main differences between Ashton’s and Maury-
Lechon’s two main groupings are:
1. in Ashton: presence (Shoreae) or absence
(Dipterocarpi) of the incrassate fruit sepal base (as
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opposed to whole calyx tube), and in most cases the
basic chromosome n-number is consistent for each
of the two groups (7 in Shoreae, 11 in Dipterocarpi),
as also are the scattered (Dipterocarpi) or tangential
bands (Shoreae) of resin canals;
2. in Maury-Lechon: some consistent characters for
each of the two groups (a), and most frequent expression
of some other characters in each group (b);
a) Three consistent characters:
• fruit-sepal base arrangement in ripe fruit: imbricate
(Imbricate group), valvate (Valvate group) or
intermediary (mainly Dryobalanops, but also
Parashorea or Stemonoporus) according to their
development from flower-bud to open flower. Sepals
are clearly imbricate before the petals develop
out of the sepal bud and remain so after the petals
have grown out of the sepal bud in the Imbricate
group. The sepals are imbricate at first and then only
retain some traces of imbrication in Dryobalanops,
Stemonoporus, Vateria, Marquesia, Monotes; imbricate
at first and then valvate in all Vatica, and
valvate all along their development in
Dipterocarpus;
• number of strata in pollen exine (3 in Imbricate
group or 2 in Valvate group, and 4 in Monotoideae
and Pakaraimoideae); basic chromosome n-number
(mostly 7 in Imbricate, 11 in Valvate, intermediary
cases), tilioid structure of exine absent (Imbricate)
or present (Valvate), and columellae shape-type T
and Y (Imbricate) or V and U (Valvate),
• in secondary wood: arrangement of vessels grouped
(Imbricate) or solitary (Valvate), resin canals in
bands (Imbricate) or scattered (Valvate) with cellular
divisions of canal formation radial (Imbricate)
or oblique (Valvate);
b) Three most frequent expressions:
• fruit: number of incrassate bases of sepals (and
number of accrescent sepals) 2 or 3 (Imbricate)
or 0 or 5 (Valvate), bases of fruit sepals free (Imbricate)
or fused (Valvate), type of pericarp tissue
rigid (Imbricate) or rigid to soft (Valvate), fruit
equatorial section circular (Imbricate) or circular
to 3-symmetric (Valvate);
• embryo: cotyledons ‘covering-piled’ (Maury 1978)
(Imbricate), neither covering nor piled (Valvate),
hypocotyl inferior or median-inferior (Imbricate),
not inferior but apical or median (Valvate);
• seedling: cotyledons bilobed (Imbricate), or entire
(Valvate), number of root-xylem poles 4 (Im-