15 Based on their main habitat, Diplazium can be included into three major
groups: dryland, riparian and rheophytic. Rheophytes are plant species which inhabit the beds of swift-running streams and rivers and grows up to flood-level,
but not beyond the reach of regularly occurring flash floods van Steenis, 1981. The rheophytic plants are characterized by having particular morphological
characters as follow: a narrow lanceolate leves or leaflets; b mattet root systems; c short erect, ascending, or creeping rhizomes tightly attached to streambed
substrates; and flexible stems and petioles. Dryland species generally do not occur in the flooded zone where rheophytes occur, while rheophytes do not occur in
dryland habitat where dryland plants thrive Imaichi Kato 1997. As pointed out by Imaichi and Kato 1997, there is distinct habitat segregation between
rheophyte and dryland species, especially in the humid tropics. Following the definition described by Lincoln et al 1982, riparian means living or situated on
the banks of rivers and streams, whereas terrestrial is living habitually on the land or ground surface.
2.3.1.1. Rheophytic of Diplazium
Rheophytic of Diplazium are smallest group of Diplazium in West Malesia. There are only two species reported in this study, viz. D. aequibasale
and D. wahauense Table 2.1. and 2.2.. Kato et al 1991 reported three species, namely D. aequibasale, D. wahaunse and D. subsinuatum. The last species
however has been moved into Deparia and treated as Deparia lancea Thunb. Fraser-Jenk based on morphology, cytology and molecular characters Sano et al
2000. In this paper D. subsinuatum is excluded. In Sumatra and Borneo, the first species are usually growing on lowland clayey stream-bank, whereas the second
species, that is only found in Borneo, growing at streambed in flood zone in lowland.
Van Steenis 1981 classifies rheophytes into obligate and facultative, according to preference for rheophytic habitats. In Borneo, many plants of D.
esculentum are growing well on river banks in the flood zone, for example at
Sungai Joloi track to Batikap, Central Kalimantan. This species may be included in facultative rheophytes. But anatomical observations show that leaves
16 of D. esculentum have poorly developed intercellular spaces of rheophytes Kato
Imaichi unpublished, there is no distinct morphological difference between the reophytic and dryland plants. Kato 1991 regarded such species as evolutionarily
incipient rheophytes. Kato et al 1991 assumed that most rheophytes are products of primary
speciation from dryland mother species. Diplazium wahauense presumably derived from D. riparium, Deparia biserialis and De. confluens from D.
petersenii, Phronephrium hosei from P. rhombeum or P. menisciicarpon.
2.3.1.2. Riparian Diplazium
Only few species occur on river banks or stream. They are D. aequibasale
, D. riparium, D. fuliginosum, D. lomariaceum and D. porphyrorachis Table 2.2.. However these species do not strictly grow at this habitat. The last
three species are more usual growing in dryland of shady ravine in the forest. In Borneo, much of individual plants of D. riparium are also growing well in shady
dryland. All species mentioned above, are usually found on lowland mountain forest.
Environmental condition seems very important component of speciation in Diplazium
although this of course depend upon of how one of species response the ecological change. Diplazium riparium and its closely related species D.
aequibasale and D. wahauense may be a good example for it. Kato et al 1991
presumed that D. wahauense may have been derived from D. riparium which occurs in riparian and dryland forest of Borneo. As they explained and supported
by this studies see Chapter 8, these two species share black scales, somewhat crisped, entire scales, blackish stipes, dark brown, naked rachises, and
imparipinnate leaves with 4 pairs of entire lateral pinnae. Diplazium wahauense differs from D. riparium mainly in its narrow pinnae, which are characteristic of
rheophytes.
2.3.1.3. Diplazium in Dryland
