Notes of Some Rheophytes and Riparian Species of Seed Plants in Taman Negara Kuala Tahan, Pahang

The wet and fast-flowed rivers in the lowland and hill forest at Taman Negara provide a suitable habitat for the rheophytes and riparian flora of seed plants. Fourteen species of rheophytes and riparian are listed and discussed in this paper, of which some taxa are locally common along the riverbanks of Sungai Tahan and Sungai Tembeling.


Introduction
The complex terrestrial ecosystem on earth covers many unique ecosystems from the tropical rain forest to tundra. Among them is the riparian forest which is one of the biosphere's most complex ecological systems [1] [2]. The term 'riparian' derives from a Latin word 'riparius' meaning "of or belonging to the bank of a river" and refers to biotic communities living on the shores of streams, rivers, ponds, lakes, and some wetlands [3]. The complexity of riparian forest which has an influence on the pattern of seasonal flooding, flowing river water and fertile soils was reported in various studies such as by Naiman and Décamps [2] and Miller [4]. This forest zone has a high diversity with vascular plants species which relate to frequency of floods, topography, soils, variation in climate and disturbance scale [5].
In Peninsular Malaysia, riparian forests are the edaphic vegetation which occur in the river mouth of mangrove forest up to the montane forests [6]. The structure and composition of the forest are very complex and dependent on the influence of tide and subsidence, flow rate of river flows, tributary widths, riverbank height and diversity of flora that populate this habitat [7].
Certain species of plants have special adaptions to the wet condition and fast-flowed current stream. These species are called riparian species and rheophytes. A rheophyte is an aquatic plant that lives in fast moving water currents in an environment where few other organisms can survive.  Tahan, which is drained by several important rivers such as Sungai Tahan, and Sungai Tembeling, is also inhabited with many taxa of riparian and rheopytes species (Figure 1). The complete account of rheophytes in the world was given by van Steenis [8]. In this paper, we have listed some species of riparian and rheophytes which were gathered from the previous herbarium collections and our short survey along Sungai Tahan and Sungai Keniam in September 2020.

Materials and Methods
During the scientific expedition in September 2020, we made a short survey along Sungai Tahan and Sungai Keniam to collect the data of rheophytes and riparian species of seed plants. Then, the status of riparian and rheophytes species was confirmed from previous literature such as Tree Flora of Malaya [9] [10] [11] [12], Forester's Manual of Dipterocarps [6], Rheophytes of the World [8], Flora Malesiana [13] [14]. We also examined the herbarium specimen lodge in the herbarium of Forest Research Institute Malaysia (KEP), herbarium of University of Malaya (KLU), herbarium of Universiti Kebangsaan Malaysia (UKMB) and herbarium of Rijksherbarium (L). Additional information from the herbarium labels such as the habits, general morphology, and occurrence of the taxa in their locality were also extracted.
A B Figure 1. Riparian forest along Sungai Tahan at Taman Negara. A. The sand deposition on the riverbanks and the occurrence of lowland rain forest behind the riparian forest. B. Rocky stream bed which is suitable for certain rheophyte species such as Ficus ischnopoda and Syzygium salictoides.

Results and Discussion
A total 12 species of rheophytes and two species of riparian flora were listed in this study. The figures of all rheophyte species are shown in Figure 2-5 while for riparian species are shown in Figure 6. Syzygium comprises four species out of five species of this genus in Peninsular Malaysia which are categorized as rheophytes [15]. Another species, Syzygium rheophyticum is considered as very rare and only recorded in Terengganu. The species from Meliaceae, viz. Aglaia yzermannii and Dysoxylum angustifolium are two species that can grow together and greatly resemble each other in general form [8] and commonly confused in the field. But the former species have lesser stature, smaller, imparipinnate leaves with fewer leaflets, tiny flowers, and small indehiscent orange-pink fruits each with 2 seeds [14]. The latter have more stature, paripinnate leaves with more leaflets, larger flowers, and capsule splitting fruits with 2-6 seeds [13]. Ficus ischnopoda is solely rheophytes in genus Ficus [8]. This species inhabits the rocky streams as reported in previous studies in Peninsular Malaysia such as in Tembat Forest Reserve [16] and Gunung Basor Forest Reserve [17]. Based on the first author's personal observation, this species was also found in Sungai Sedim Recreational Forest, Kedah, Gunung Tebu Forest Reserve, Terengganu and Ulu Sat Forest Reserve, Kelantan. The riparian species of Dipterocarpus oblongifolius is common in all rivers in east coast of Peninsular Malaysia and usually leaning across the rivers. Henderson [18] reported that 87 species of epiphyte (mainly orchids and ferns) were recorded in a single stem of D. oblongifolius. The unique observation was reported by Ahmad Fitri [16] in Tembat Forest Reserve which Dipterocarpus oblongifolius trees was not found in the upper stream as a lot of rare species of Altingia excelsa trees recorded. Meanwhile, the number of A. excelsa has decreased in the lower stream whereby the D. oblongifolius is dominant. Ficus obpyramidata is also a common riparian species in Peninsular Malaysia in the lowlands to lower montane forest [19]. A study by Ahmad Fitri [20] also found out that this species is common along the riverbanks of Sungai Kuantan in Remen Cereh Forest Reserve, Pahang. Taxon description: A small tree 3-5 m tall with broad irregular crown. Bark pale brown. Branches from near the base, usually patent and projecting horizontally from the riverbank over the water, sometimes ascending. Twigs slender, with numerous to densely covered with brown or yellowish-brown stellate scales, especially towards the apex. Leaves 14.0-30.0 cm long, imparipinnate; leaflets blade linear, linear-lanceolate, or narrowly lanceolate, leathery, 3.0-16.0 cm x 0.5 cm -3.0 cm, slightly curved, petiolules 0.2-0.7 cm long, rachis and petiolules with few to numerous scales like those on the twigs; apex acuminate or caudate, base cuneate, glabrous or with a few scales on lower surface, particularly along the midrib secondary nerves 9-17 pairs. Male inflorescence up to 17 cm long and 12 cm wide; peduncle up to 1 cm, peduncle, rachis, branches, and pedicels with numerous to densely covered with scales like those on the twigs. Male flowers, small, c. 0.1 cm in diam.; pedicels up to 0.1 cm. Calyx densely covered with stellate scales on the outside. Petals 5; anthers 5, broadly ovate, inserted just below the margin of the tube. Female inflorescence and flowers similar to those of the male but the inflorescence smaller, flowers fewer, up to 2 mm in diam, pedicels up to 0.2 cm. Infrutescence up to 15 cm long. Fruit ellipsoid or subglobose, indehiscent, orange-brown or orange-pink during fresh, densely covered with stellate scales like those on the twigs; inner surface of pericarp pink 2.0 cm x 2.0 cm, 1-2 locules, each containing 1 seed, aril translucent. Distribution in Peninsular Malaysia: Perak, Kelantan, Terengganu and Pahang. Habitat: On the banks of rocky rivers. Panell [14], stated that this species is found mainly in the Malay Peninsula where it seems to be restricted to the banks of relatively deep stretches of otherwise stony, fast flowing rivers. Local names: Bekak Uses: According to Burkill [21], the Semang people in Kuala Lipis, Pahang, pound the leaves in cold water and use the extract to wash the body after childbirth. The arils are edible [14].

Notes:
The only rheophytic from Aglaia in Peninsular Malaysia [22]. Common along the riverbanks in Taman Negara Kuala Tahan. Taxon description: A much branch bush to 2 m tall without buttresses. Exudate slight, yellow coloured. Twigs 4-angled, pale brown when dry. Terminal bud narrow and pointed, minutely reddish tomentose, 0.4-0.5 cm long. Leaves narrow lanceolate, subcoriaceous, petiole short, apex acuminate, base tapered, 3.0-11.0 cm x 0.5-2.5 cm, both surfaces rather dull brown when dry, the lower surfaces paler. Venation obscure below, ridge and furrowed; midrib raised on both. Inflorescences in racemes, short and compact, few-flowered, mostly from the upper leaf-axils, rachis tomentose, pedicels slender, tomentose, flowers small, outer sepals broadly ovate acute, slightly pubescent outside, inner sepals narrowly obovate, 0.4-0.5 cm long, petals 0. Fruit small, ellipsoid-globose to globose, 0.8-0.9 cm long, on a slender pedicel, 1 cm long, orange or green during fresh, drying pale reddish, brown or bluish mauve, pericarp thin and brittle.   . Notes: Very common along Sungai Tahan. According to [23], the seeds are locally used as bait for fishing. Mabberley and Pannell [22] believed that the seed of this species are dispersed by fish. So, the fish flesh also has a strange flavour after ingestion of the seeds [24] [13].      [25] mentioned that this taxon is rare and only known in Sungai Tahan (Pahang). Additional localities have mentioned by van Steenis [8] whereby this taxon was also recorded at Sg Kerbat and Sg. Terengganu in Terengganu.

Conclusion
The riparian habitat around the riverbanks of Taman Negara is inhabited by the species of rheophytes and riparian. Further studies would be needed to expand the list of the species and determine the stand structure as well as the phenology and ecological studies.