A revision of Dissochaeta (Melastomataceae, Dissochaeteae)

Abstract Dissochaeta is a plant genus of woody climbers, classified in the tribe Dissochaeteae (Melastomataceae). The taxonomic history of the genus is complicated and includes some allied genera like Dalenia, Diplectria, Macrolenes and Omphalopus. Most of them are already regarded as synonyms of Dissochaeta except for Macrolenes which is considered a separate genus here as well. Dissochaeta is characterised by its scrambling habit, interpetiolar outgrowths, 4-merous flowers, dimorphic stamens and berry-like fruits. A taxonomic revision of Dissochaeta is presented, which includes references, a complete list of synonyms, detailed morphological descriptions of the species and an identification key, as well as information on the distribution, habitat and ecology, vernacular names, notes and lists of examined specimens. Fifty four species and two varieties of Dissochaeta are recognised. We designate several lectotypes, propose eleven new combinations and we describe one new species and one new variety.

The genus is characterised by its scrambling growth habit, opposite phyllotaxy with interpetiolar outgrowths, terminal or rarely axillary inflorescences, 4-merous flowers, 2-whorls of dimorphic stamens and berry-like fruits. Some species are restricted both geographically and elevationally, while others are widespread. The genus Ma crolenes Naudin closely resembles Dissochaeta and also consists of woody climbers with a scrambling habit, but differs in some vegetative and flowering aspects. Together with Macrolenes, Dissochaeta is included within Tribe Dissochaeteae (Naudin) Triana (Tri-ana 1872, Cogniaux 1891, Bakhuizen van den Brink f.1943, Maxwell 1984. On the other hand, the genus is also considered as part of tribe Miconieae (Blume 1831a, 1831b, Don 1832, Endlicher 1840, Naudin 1851, Miquel 1855, Renner 1993. Taxonomic revisions for parts of the genus and its allies can be found in Bakhuizen van den Brink f. (1943), Veldkamp et al. (1979), Nayar (1980) and Renner et al. (2001).

Taxonomic history
Dissochaeta was first proposed by Blume (1831a) and consisted of 15 species with eight of them split off from Melastoma L. (in its wide sense: Jack 1823, Blume 1826, De Candolle 1828. The word Dissochaeta is derived from the Greek words "dissos", meaning double and "chaitè", meaning hair or bristle and alludes to the two filiform appendages at the base of the anthers (Backer 1936, Maxwell 1980a, Kartonegoro and Veldkamp 2010. This feature is present in most of the species, but absent in a few. Blume (1831a) proposed two sections in the genus, section Dissochaeta and section Diplectria Blume, which differ in the shape of the calyx tube, the appendages at the base of the anthers and the indumentum of the ovary apex. Section Dissochaeta has a cyathiform calyx tube, 4-dentate calyx lobes and an apically pubescent ovary, while section Diplectria has a cylindric calyx tube, truncate lobes and an ovary with a glabrous apex (Blume 1831a(Blume , 1831b. Section Dissochaeta was subdivided by Blume (1831a) into three informal groups, a) Tetrandrae, flowers with 4 stamens, without any staminodes; b) Octandrae flowers with 4 stamens, alternating with 4 staminodes; and c) Octandrae flowers with 8 fertile stamens (Maxwell 1980a, Kartonegoro andVeldkamp 2010). Blume (1831a) also described the new genus Aplectrum Blume, comprising three species, which have an ovate-globose calyx tube and four stamens alternating with four staminodes. The anthers of Aplectrum were said to be inappendiculate, unlike the appendiculate anthers of Dissochaeta (Blume 1831a). Blume did not indicate the similarity/difference between Aplectrum and Dissochaeta sect. Diplectria, which also has four staminodes alternating with four stamens. He also did not mention the position of the fertile and sterile stamens in relation to the position of the petals, a character later used to separate genera (Maxwell 1980a). Later, Reichenbach (1841) raised section Diplectria to genus level as Diplectria. Simultaneously with the establishment of Dissochaeta and Aplectrum, Blume (1831a) established Marumia Blume (=Macrolenes), also a woody climber, but different in having axillary inflorescences, persistent and long calyx lobes, eight fertile stamens and several filiform appendages at the base of the anthers. Korthals (1844) accepted Blume's Dissochaeta and Aplectrum as distinct groups of woody climbing genera in Melastomataceae in his Netherland Indies (Indonesia) Melastomataceae account. He proposed a new woody climber genus, Dalenia Korth., which has similarities with Dissochaeta, but instead has a deciduous calyptra which encloses the petals before anthesis. Naudin (1851) included Diplectria in Dissochaeta and made a new division of the genus into two groups without any nomenclatural status, Inermes Naudin and Bisetosae Naudin, which differ from each other in lacking or having bristle appendages at the base of the anthers, respectively. The Inermes group has similarities with Blume's Diplectria and Bisetosae with Blume's Dissochaeta. Furthermore, Naudin (1851) maintained the genera Aplectrum and Dalenia and he also proposed a new genus, Omphalopus Naudin, with 3 species defined by having filaments attaching to the anthers in the middle (medifixed) and a tessellate surface of the locules (Naudin 1851).
The name Aplectrum is a later homonym of Aplectrum (Nutt.) Torr., already proposed by Torrey (1826) for a subgenus of Corallorrhiza (Orchidaceae) by Nuttal (1818). Therefore, Gray (1854) introduced the new name Anplectrum A.Gray as a valid genus name for Blume's Aplectrum, which was followed by Triana (1872) in his World Melastomataceae account by uniting all species of Diplectria and Aplectrum within Anplectrum.
Cogniaux (1890,1891), in his monograph of the family, accepted Triana's (1872) concept and rejected Baillon's generic classification (1877). He reinstated several genera and divided Dissochaeta into three sections, sect. Diplostemones Cogn. (invalid name, should have been section Dissochaeta; Kartonegoro and Veldkamp 2010), with a truncate or obscurely lobed calyx and eight stamens with elongate appendages; sect. Isostemones Cogn., with a similar calyx but with four stamens with elongate appendages; and sect. Dissochaetopsis Cogn., with long, linear to lanceolate, caducous calyx lobes and four straight stamens with short appendages. Cogniaux's classification of Dissochaeta and allied genera were adopted by Krasser (1893) except that he synonymised Anplectrum with the older genus Diplectria. The number of infrageneric taxa increased when Merrill (1917) proposed the new species Dissochaeta glabra Merr. and placed it in a new section Disparistemones Merr.
Bakhuizen van den Brink f. (1943), in his comprehensive work on the Melastomataceae of the Malay Archipelago (Malesian Region), did not adopt an infrageneric classification for Dissochaeta, quite unlike previous authors. Thus, he described some new species in Dissochaeta and established two new woody-climbing genera, Backeria Bakh.f. and Neodissochaeta Bakh.f., based on the small size of the calyx tube and the presence of narrow extra-ovarian chambers, respectively. Like Cogniaux (1890Cogniaux ( , 1891, he also maintained the genera Dalenia and Omphalopus as distinct genera. He discussed the possible illegitimate character of the name Anplectrum, which he considered to be a superfluous orthographic variant of Aplectrum (both bad Greek) and he preferred to regard Diplectria and Backeria as accepted names instead (Bakhuizen van den Brink f. 1943). Nayar (1966Nayar ( , 1969b considered Neodissochaeta as a distinct genus and added some new species to it. The genus Backeria was also maintained by Raizada (1968), but he synonymised all species of Diplectria with it. However, since Diplectria is an older name than Backeria, Diplectria is the correct generic name ) in this circumscription. Maxwell (1980a divided Dissochaeta into only three sections: sect. Dissochaeta, sect. Anoplodissochaeta and sect. Omphalopus. This separation is mostly based on floral characters, especially the stamens. Section Dissochaeta has well-developed calyx lobes (>2 mm long) and curved stamens, while sections Anoplodissochaeta and Omphalopus have undeveloped calyx lobes (<2 mm long) and straight stamens. Section Omphalopus differs from sect. Anoplodissochaeta by having tessellate-reticulate locules (vs. smooth ones) and medifixed anthers (vs. basifixed). In agreement with Bakhuizen van den Brink f. (1943) and Veldkamp et al. (1979), he also maintained Diplectria as a distinct genus allied to Dissochaeta with Backeria synonymised under it and he included Dalenia, Neodissochaeta and Omphalopus in Dissochaeta.
Results of molecular phylogenetic studies by Clausing and Renner (2001) showed that a woody climbing or scrambling growth habit evolved only once in the Asian Melastomataceae. Based on that result, Renner et al. (2001) recognised only the single genus Dissochaeta, with two other genera, Diplectria and Macrolenes, as synonyms.  ignored the differences in floral characters. Macrolenes, sister to Dissochaeta , differs from Dissochaeta in a unique combination of vegetative and floral characters (presence of a pair of hair cushions at the base of the lower leaf surface, axillary inflorescences, long and persistent calyx lobes and the anthers with several basal filiform appendages) and is, therefore, considered to be a distinct genus, separate from Dissochaeta (Bakhuizen van den Brink f. 1943, Nayar 1980, Maxwell 1984.

Circumscription of Dissochaeta proposed in this study
Diplectria is here considered to be a synonym of Dissochaeta since both genera have correlating floral characters with intermediates between the extreme forms. This concept of Dissochaeta, including Diplectria, was already pointed out by Backer (Bakhuizen van den Brink f. 1943), following Naudin's concept (Naudin 1851). Dissochaeta and Diplectria show a strong morphological similarity (Bakhuizen van den Brink f. 1943, Veldkamp et al. 1979, Maxwell 1984 in their the scrambling habit and terminal inflorescences with 2-5 ramifications, but were distinguished based on floral characters like the position of the stamens and staminodes on the hypanthium ). According to Maxwell (1984), Diplectria differs from Dissochaeta in having four fertile stamens opposite the petals (oppositipetalous) and four staminodes alternate to the petals (alternipetalous). In contrast, in Dissochaeta the alternipetalous stamens are always fertile, while the oppositipetalous stamens are either fertile, staminodes or absent. Based on these differences, these two genera were even classified in two different subtribes, Diplectrinae J.F.Maxwell and Dissochaetinae Naudin (Maxwell , 1984. However, there are strong similarities between Dissochaeta and Diplectria in the structure of the stamens: their position in bud, connective appendages and the direction and shape of the alternipetalous stamens. The oppositipetalous stamens of Diplectria also similar to those of Dissochaeta. The shape and orientation of the oppositipetalous stamens in Dissochaeta beccariana Cogn., Dissochaeta glandulosa Merr., Dissochaeta laevis Ohwi ex J.F.Maxwell and Dissochaeta sarawakensis (M.P.Nayar) J.F.Maxwell are similar to those of Diplectria. These four Dissochaeta species also have a pair of glandular patches abaxially on the base of the leaf blades, which is also found in several species of Diplectria and, therefore, they are considered as intermediate between the two genera and which are here regarded congeneric because of the resulting continuous morphological variation.
Dalenia was distinguished from Dissochaeta based on the presence of a calyptra enclosing the petals in bud (Korthals 1844, Naudin 1851, Miquel 1855, Triana 1872, Cogniaux 1890, Krasser 1893, Bakhuizen van den Brink f. 1943, Nayar 1966). The calyptra is in fact the hypanthium/calyx and it falls off when flowers are mature. Despite this calptriform hypanthium, the habit, position of the inflorescences, stamen characters and the baccate fruits are highly similar to those of Dissochaeta and Diplectria within the tribe Dissochaeteae (Nayar 1966). As the inflorescence position and the stamen characters are considered to be more important characters for the recognition of genera, the presence of the calyptra is regarded as a variation within the genus and Dalenia is considered as congeneric with Dissochaeta in this revision following Maxwell ( , 1984 and Renner et al. (2001).
Omphalopus was also distinguished from Dissochaeta by its tessellate reticulate anthers with medifixed filament attachments (Naudin 1851, Miquel 1855, Triana 1872, Cogniaux 1890, Krasser 1893, Bakhuizen van den Brink f. 1943). This unusual insertion seems to be insufficient for separating the genus and since the habit, leaves arrangement, inflorecences, calyx tube and fruits resemble those of Dissochaeta, it may by considered as a synonym , Kartonegoro and Veldkamp 2010.
Macrolenes was also known to have similar habit and ecological aspects with Dissochaeta. The genus also grows as woody climbers with a scrambling habit, but differs in some vegetative and flowering aspects with Dissochaeta. Macrolenes can be distinguished from Dissochaeta by a combination of some characters, e.g. axillary inflorescences (vs. mainly terminal in Dissochaeta), a pair hair cushion domatia on the base of abaxial leaves (vs. cushion domatia absent), longer and distinct calyx lobes (vs. mainly shorter and often indistinct calyx lobes) and several fimbriate, filiform appendages on the alternipetalous anthers (vs. only a pair of filiform, non-fimbriate appendages on the alternipetalous anthers). Some species of Dissochaeta have long calyx lobes, similar to those of Macrolenes, but they are usually erect, not reflexed and mostly fall off when fruiting. Based on those constant differences in morphological characters between two genera, here we agree to keep Macrolenes as a separate genus from Dissochaeta.
Fifty four species and two varieties are recognised in this revision. Species delimitations are based on clear morphological discontinuities in more than a single character. Specific characters used for recognition are shown in the descriptions, notes and the porting, long internodes and pendent flowering and fruiting branches (Maxwell 1984, Kartonegoro and Veldkamp 2010. In some species, adventitious roots are also common, which lignify and become hook-shaped structures after desiccation .

Branchlets
The branchlets are usually terete and rarely angular, though, in some taxa. angular branchlets become terete when older. The indumentum of the branchlets is variable, ranging from subglabrous, glabrescent or covered with sparse or dense stellate hairs with a punctate, furfuraceous, tomentose, or floccose appearance. In addition, some species also have short or long, dense, simple, glandular or eglandular bristle hairs. Mature branches are usually glabrescent.

Nodes
Nodes of all species bear some kind of large and swollen interpetiolar outgrowths (stipules are unknown in the family), which vary from just lines and ridges to crest-like and often annular outgrowths (Fig. 2). In some species, such a D. glabra Merr., D. glandiformis J.F. Maxwell, D. pulchra (Korth.) J.F.Maxwell, D. sarawakensis and D. stipularis (Blume) Clausing, the interpetiolar outgrowth is conspicuous and wide, which may help climbing and stabilisation in the same way thorns or hooks do in other scramblers . The indumentum of the nodes is similar to that of the branchlets, but denser.

Leaves
Like in most Melastomataceae, the phyllotaxis in Dissochaeta is opposite in one row (distichous, never decussate) with equal-sized (isophyllous) leaves. The shape is quite variable from ovate, elliptic to oblong or combinations of these within species. The apex usually is acuminate with a varying tip length. The margin is generally entire and becomes wavy when dry except for D. pulchra and D. rectandra Karton., which have a slightly serrulate margin. The leaf base varies between rounded, subcordate to shallowly cordate with distinct sinuses. The venation of the leaves is acrodromal with a midrib at the base and one or two pairs of major secondary (lateral) veins. Another pair of lateral veins also arises from the base and runs along or merges with the leaf margin and forms an intramarginal vein. In general, there are numerous secondary veins and a reticulate pattern of finer, higher order veins (Maxwell 1984). The main veins are usually sunken adaxial and raised on abaxial. Most species have a dark glossy, glabrous adaxial leaf surface except in some species, e.g. D. hirsutoidea Furtado, D. porphyrocarpa Ridl. and D. rostrata Korth., which are hispid and covered by sparse or dense bristle hairs. On the abaxial surface, the indumentum varies amongst the species from glabrous to stellate puberulous to furfuraceous, tomentose, floccose or setose with glandular or eglandular bristle hairs. Unfortunately, the leaves are usually not sufficient for definitive determina-tions and many species of Dissochaeta require flowers or fruits for identification because many vegetative characters are generally shared by two or more taxa.
A pair of peculiar thin walled corky cushions at the base of the leaf blades on the abaxial surface, called "glandular patches", are found in species like D. beccariana, D. glabra, D. glandulosa and D. laevis. This feature resembles a pair of hair cushions at the base of the leaf blades on the lower surface in Macrolenes. Their function, if any and homology with domatia, are unknown (Maxwell 1984).

Hypanthium and calyx
Like in most Melastomataceae, the receptacle forms a tube, the hypanthium, with calyx lobes at the apex, alternating with whorls of petals and stamens (Hansen 1984). The shape of the hypanthium varies from campanulate, urceolate, tubular to cyathiform or funnelform and can be terete or angular. The size of the hypanthium also varies from small (2-4 mm long) in D. biligulata, D. glabra var. glabra and D. gracilis (Jack) Blume to large (8-10 mm long) in D. axillaris. The indumentum of the hypanthium ranges from glabrous to stellate-furfuraceous to tomentose to floccose with or without scattered to dense bristle hairs. This indumentum is important to identify certain species (Maxwell 1984). The presence of eight vertical ridges on the hypanthium is typical for species like D. leprosa (Blume) Blume, D. pallida (Jack) Blume and D. spectabilis J.F. Maxwell. There are four calyx lobes, but these are not always visible as the calyx of most species may be truncate, undulate or have four small points. Calyx lobes can be rounded or triangular as in D. annulata, D. atrobrunnea and D. leprosa or can be linear to long, lanceolate as in D. johorensis Furtado, D. macrosepala Stapf and D. porphyrocarpa. The lobes are important for identification. The indumentum of the calyx lobes is similar to that of the hypanthium.

Petals
As the flowers are 4-merous, four free petals are commonly present. The petals are usually contorted in bud and overlap. The petal bud is always conical with an acute or acuminate tip, but some are rounded in D. fallax (Jack) Blume. The petals are thin, conspicuous, symmetric and colourful. Even though the colour of the petals generally has very little taxonomic value, in some cases the constant colour of the petals is useful to distinguish the species. The most frequent shapes are ovate, obovate and suborbicular with rounded or obtuse to acute tips and a clawed base. In a few species, the margin and tip of the petals are somewhat bristly, e.g. D. hirsutoidea, D. johorensis, D. malayana Furtado and D. porphyrocarpa. The petals are reflexed or erect.

Stamens
The stamens provide the best taxonomic characters for identification (Kartonegoro and Veldkamp 2010). In most species, 8 heterantherous stamens are usually present in two, dimorphic staminal whorls, an outer, alternipetalous and an inner, oppositipetalous one (Maxwell 1984, Kartonegoro andVeldkamp 2010). The alternipetalous stamens are known as the pollinating stamens and the oppositipetalous (alternisepalous) ones are the feeding stamens (Kadereit 2006, Kartonegoro andVeldkamp 2010). Most species have 8 fully developed and complete fertile stamens; in some species only 4 fertile stamens developed with the other 4 stamens being staminodial or absent.
The filaments are well-developed, flattened, glabrous and uniform in shape. Their length and orientation vary with the stage of maturity of the stamens. The filaments originate at the same level below the inner margin of the hypanthium. In both anther types (alternipetalous and oppositipetalous) before anthesis, the filaments are abaxial (facing outside) and the anthers adaxial (facing towards the inside) (Fig. 3I, II). The filaments alternating with the petals are straight and the point of attachment with the anthers distinct, while those opposite the petals are sharply bent and incurved before reaching the rather indistinct point of attachment with the anthers. Distally there is a sharp bend shortly below the attachment to the anther, the stipopodium ( Fig. 3d) . When dissecting the filament, it disarticulates and breaks here easily, although the "natural" point of breakage is apparently between the stipopodium and the connectival area of the basal crest and lateral appendages . The attachment of the filament to the anther is usually near the base (basifixed) except in D. fallax where the filament is inserted in the middle part of the anther (medifixed). In bud, the stamens are inserted at the inner margin of the hypanthium, either in the extra-ovarial chambers or not.
The anthers are elongate, subulate and glabrous and open distally with a single pore. In mature flowers, they reverse their orientation by bending upwards and become less apical to the filaments. Filaments become longer and curve sideways or straight upwards. The stipopodium of mature oppositipetalous stamens becomes flexed to sinuate and leaves a scar-line, thus the filament and anther are not in parallel alignment (Maxwell 1984). The anthers here are more or less hook-to S-shaped, while the alternipetalous anthers are usually curved, sickle-shaped (Fig. 4a). In a few species, the orientation of all anthers is straight, e.g. D. bakhuizenii Veldkamp, D. inappendiculata Blume and D. vacillans (Blume) Blume (Fig. 4b). The oppositipetalous anthers are usually thicker and shorter than the alternipetalous ones. Their thecae are smooth and glabrous except in D. fallax where they are tessellate-reticulate.
The connective of the alternipetalous anthers can be sterile, without thecae, in the basal part. This sterile zone is the pedoconnective and is found in some Melastomataceae and varies in size relative to the size of the stamens (Kadereit 2006, Wong 2016). In the oppositipetalous anthers, a pedoconnective is rare or not developed. The base of the pedoconnective usually has basal appendages (basal crest), which are membranous and triangular, hastate, oblong or ligular in shape. Lateral appendages are solitary or paired, filiform to ribbon-like and sometimes divided at the tip (Kartonegoro and Veldkamp 2010). The two appendages in oppositipetalous anthers extend from the lower part of the thecae and are adaxially bifid, ligular, or have spuriform appendages and, laterally or basally, there may or may not be a pair of filiform appendages.

Pollen
Although the stamens of Dissochaeta are diverse and display many different shapes and orientations, the pollen is uniform and is not of much taxonomic use. It has been described as 3-colpate with the colpi alternating with three pseudocolpi, prolate, 14-20 × ca. 11 µm, with a psiIate or smooth exine (Maxwell 1984).

Staminodes
Staminodes are found in several species of Dissochaeta. Species included in Diplectria by Bakhuizen van den Brink f. (1943), Veldkamp et al. (1979) and Maxwell (1984) have staminodes in alternipetalous stamen whorl. They have anthers with undeveloped thecae, which are terete, ligular or triangular and infertile and lack the pedoconnective. However, the filaments, basal crest and lateral appendages are well developed, similar to the fertile alternipetalous stamens that are present in many species. These staminodes are functional in order to increase the attraction of the flowers by their colourful appendages and they might signal a large amount of available pollen (Kadereit, person. comm.). Oppositipetalous staminodes are different and have small thecae, ± ⅓ of the length of the alternipetalous ones with minute or well developed connective appendages and with or without lateral appendages. Differing from those previously, it seems that these staminodes are just stamen rudiments without function (Kadereit, person. comm.).

Gynoecium
The height of the ovary ranges from about ⅓ to nearly the length of the hypanthium. The ovary is glabrous, villous or has several bristly hairs at the tip where it joins with the style. The ovary apex is usually rounded or conical to mammiform in a few species, like D. bakhuizenii and D. nodosa Korth. The placentation in Dissochaeta is similar to that of the other genera in the tribe (except for a few Creochiton species, Kartonegoro and Veldkamp 2013), with a single placenta in each of the four locules, axillary attached to the middle of the central column. The style in bud is straight, but slightly curved at maturity, especially at the apex. The curved orientation of the mature style is usually opposite to that of the filaments. In the heterantherous species like D. divaricata (Willd.) G. Don, D. glabra and D. viminalis, the filaments of the two whorls are bent differently (Kadereit, person. comm.). The style is glabrous except in a few species where it is pubescent. The stigma of all species is capitate, but minute and inconspicuous.

Extra-ovarial chambers
Between the hypanthium and the ovary, there are usually septa which form between the chambers. These chambers are known as extra-ovarial chambers and the stamens develop from here (Bakhuizen van den Brink f. 1943, Hansen 1984, Maxwell 1984, Kartonegoro and Veldkamp 2010. The number and depth of these extra-ovarial chambers depend on the number and size of the fertile stamens. Usually, there are 4 or 8 chambers, which vary from shallow to reaching the base of the ovary (Kartonegoro and Veldkamp 2010). The depth of the chambers was used by Bakhuizen van den Brink f. (1943) to separate Backeria and Neodissochaeta from Dissochaeta.

Fruits
The fruit in Tribe Dissochaeteae, including Dissochaeta, is baccate (berry) with mainly a subglobose, ovoid to urceolate shape. The indumentum resembles that of the hypanthium. The colour is green at first, then becomes dark blue to purple when ripe. Some species like D. biligulata and D. gracilis have 8 distinct lines on the surface of the fruits, while in D. leprosa and D. spectabilis, 8 ridges are also common. When fruiting, the remnants of the calyx lobes are sometimes persistent in an erect or downward reflexed position or they fall off. Seeds have a cuneate shape, are smooth and flat-topped.

Distribution and ecology
Dissochaeta is distributed in South China to South-East Asia, mainly the Malesian region, including the Nicobar Islands (India). It is found north and south of the equator along the South-East Asian tropical rainforest belt but is absent in the eastern part of the Lesser Sunda Islands (Flores, Sumba and Timor). Borneo is the centre of diversity of the genus with 26 species of which 17 are endemic. From the Philippine Islands to New Guinea, the number of taxa and their abundance declines. The occurrence of the genus in mainland India is questionable (see note under D. divaricata).
Dissochaeta is found mostly in tropical evergreen and perpetually wet forest with little or no seasonal variation in temperature and rainfall (Maxwell 1984). The species are found predominantly in secondary vegetation or more open places within the primary vegetation, such as tree fall gaps, river margins and roadsides. They climb several metres high and produce their flowering and fruiting branches over the tops of trees and larger shrubs. The genus has nodes which bear large interpetiolar outgrowths, which may help climbing and stabilisation in the same way thorns or hooks do in other scramblers . According to Clausing and Renner (2001), Dissochaeta has a faster growth rate than other scramblers and often outcompetes them. The climbing habit is reflected in the very wide wood vessels for hydraulic conductivity and thin-walled fibres for limited mechanical support (Van Vliet 1981). These woody climbers apparently only flower when mature and only on the branchlets which are in an exposed, open position. Branchlets that are not exposed to direct sunlight, regardless of their maturity or height in the forest, do not produce flowers (Maxwell 1984).
The majority of species and varieties revised here are confined to lowland and hilly areas up to 1500 m elevation; however, some taxa are restricted to lowland or montane forest. Some species from the lowland forest are usually found in mixed dipterocarp forest, heath forest or swampy forest. Species occuring in montane forest are D. alstonii M.P. Nayar, D. celebica Blume, D. intermedia Blume, D. leprosa, D. marumioides Cogn., D. nodosa, D. rectandra and D. spectabilis, which can reach from 1200 to ca. 2500 m altitude. There is no specific flowering and fruiting season, the species flower and fruit throughout the year. Some taxa, like D. biligulata and D. gracilis, sometimes have flowers and fruits together in the same inflorescence. Individual mature plants that reach the canopy or another suitable open area, regularly flower and fruit, but concurrently with many other individuals of the same species. This suggests that flowering and fruiting may be random, but is perhaps cyclic and may, therefore, be regulated by various environmental factors (Maxwell 1984 Islands (Flores, Sumba and Timor). Borneo is the centre of its distribution with almost 50% of the species. Some species also have a restricted distribution.
Ecology. The genus is found predominantly in secondary vegetation or more open places within the primary vegetation, such as tree fall gaps, river margins and roadsides (Kadereit 2006) in evergreen forest, mixed dipterocarp forest, heath forest, hilly forest, swamp forest and montane forest. The plants climb several metres high and produce their flowering and fruiting branches over the tops of small trees and larger shrubs at the end of branches that are in the open.

Key to species of Dissochaeta
Distribution. Philippines. Ecology and habitat. Open shade, along ridges, on wet or less sandy ground in forest or secondary forest at 220-300 m elevation.

Dissochaeta angiensis
Distribution. Moluccas and New Guinea. Ecology and habitat. Lowland hill forest to lower montane forest at 50-1300 m elevation.
Notes. 1. One of the most widespread species in the Malesian Region. Surprisingly never found in mainland Sumatra, only on Simeuleu Island, Mentawai Islands, Riau Archipelago and Bangka Island. The species also does not occur in the Philippines and the southern part of Malesia (Java to the Lesser Sunda Islands); in Sulawesi, it was only found in the South-eastern Peninsula.
2. The appearance of D. annulata resembles that of D. axillaris and D. bracteata in the shape of the leaf blades and the stamens. It differs from D. axillaris by its terminal inflorescence (instead of axillary) and slightly triangular calyx lobes (instead of truncate). It is distinct from D. bracteata by its densely brown stellate-tomentose indumentum in most parts and the campanulate hypanthium, while D. bracteata is mostly glabrous with a more tubular hypanthium.
3. The establishment of varieties was initiated by Bakhuizen van den Brink f. (1943) and  and it was mostly based on inconstant characters. The variety robinsonii was based on the rather small size of the inflorescences, including the size of hypanthium and bracts compared to typical D. annulata; we consider size too variable to support the separation of taxa, especially when all the other characters are similar, e.g. indument, hypanthium shape, stamen shape. Moreover, other varieties, johanniswinkleri and setosa, are only based on a simple character such as a more setose indumentum with additional bristles on the part of flowers and fruits. Since the variation in these characters is continuous, it is better to merge these varieties into the synonymy of D. annulata. Description. Climbing up to 20 m in height. Branchlets terete, 4-6 mm in diameter, densely covered with stellate hairs and dark red-brown bristle hairs; nodes swollen, with interpetiolar ridge, thickly covered with stellate hairs and dark-red bristle hairs thickened at base; internodes 3.5-6 cm long. Leaves: petioles terete, 5-9 mm long, densely covered with stellate hairs and bristles; blades ovate, 8-11 × 4-7 cm, subcoriaceous, base cordate, margin entire, apex acuminate, densely bristly, tip 0.5-1 cm long; nervation with 2 pairs of lateral nerves and 1 pair of intramarginal nerves; adaxially glabrous with prominent nerves, abaxially with sparsely brown stellate hairs, more dense on midrib and with bristle hairs. Inflorescences terminal (many-flowered) and axillary (9-15 flowers), up to 20 cm long, up to 7 cm long when axillary; main axis angular, flattened at upper side, densely covered with stellate hairs and bristles; when terminal with primary axes up to 16 cm long with 6 or 7 nodes, secondary axes 5-6 cm long with 2 or 3 nodes, tertiary axes 0.8-1 cm long with 1 node; when axillary with primary axes, up to 5 cm long with 2 or 3 nodes, secondary axes up to 1 cm long with 1 node, tertiary axes not developed; bracts elliptic, 10-15 × 3-5 mm, densely covered with bristle hairs; bracteoles subulate, 7-9 × 1-2 mm, densely covered with bristle hairs; pedicels densely covered with stellate hairs and bristles, 2-3 mm long in central flowers, ca. 1 mm long or subsessile in lateral flowers. Hypanthium campanulate, 6-8 × 3-4 mm, densely covered with stellate hairs and bristle hairs; calyx lobes triangular, 1-2 mm long, densely covered with bristle hairs; petal bud conical, 5-6 mm long, apex bristly; mature petals ovate, 10-12 × 5-6 mm, glabrous, reflexed, base clawed, apex obtuse, white with purple flush or pinkish. Stamens 8, subequal, filaments curved sideways; alternipetalous stamens with ca. 9 mm long filaments, anthers slightly curved, sickle-shaped, thecae 8-9 mm long, pedoconnective 3-4 mm long, basal crest minute, lateral appendages paired, filiform, up to 6 mm long; oppositipetalous stamens with ca. 7 mm long filaments, anthers S-shaped, thecae 8-9 mm long, basal crest absent, lateral appendages paired, filiform, 5-6 mm long. Ovary ⅔ of hypanthium in length, apex thickened, bristly; style slightly curved when mature, 7-8 mm long; stigma minute; extra-ovarial chambers 8, the 4 alternipetalous ones extending to the base of the ovary, the 4 oppositipetalous ones extending to about the lower third of the ovary. Fruits urceolate, ca. 12 × 5-6 mm, covered with stellate hairs and dark red-brown bristles; calyx lobe remnants persistent. Seeds ca. 0.5 mm long.
Distribution. Borneo (Central Kalimantan). Ecology and habitat. Primary and secondary lowland dipterocarp forest on swampy soil and in open areas at ca. 150 m elevation.
Distribution. Borneo and Philippines (South-western Islands).

Ecology and habitat.
Primary open lowland forest or on limestone at 10-930 m elevation.
Vernacular name. Borneo: rinsim (Kinabatangan). Note. Dissochaeta axillaris is easy to distinguish from all other species by its tomentose indumentum and axillary inflorescences. Differences with D. acmura, another species with axillary inflorescences species, are the more subcoriaceous leaf blades and the   PNH n.v.).

Dissochaeta brassii
Distribution. New Guinea (Papua New Guinea). Ecology and habitat. On the edge of forests, secondary forest or road banks at 100-700 m elevation.
Ecology and habitat. Primary and secondary forests, along rivers, roads, on waste lands; usually in the lowlands, rarely up to 1460 m elevation .
Notes. 1. Dissochaeta divaricata is one of the species with the most widespread distribution in the region and it has a wide variation in the indumentum. The specimens vary from glabrous to densely pubescent on the branchlets, abaxially surfaces of the leaf blades, inflorescences axes and the hypanthium. Sometimes they also have scattered bristle hairs on these parts. The variation in bracts and bracteoles ranges from linear to lanceolate, leaf-like. The acuminate tip of the petal bud is a good character for recognising the species and for distinguishing it from other species, e.g. D. barbata and D. conica.
Distribution. Peninsular Malaysia. Ecology and habitat. Lowland primary forest in open places at 27-120 m elevation. Note. 1. The appearance of the hypanthium with distinct calyx lobes was recognised by Nayar (1980) as typical for Macrolenes, but the character of the stamens and its appendages closely resemble Dissochaeta, with a pair of filiform appendages on the alternipetalous stamens and not fimbriate appendages as is common in Macrolenes. This species resembles Macrolenes echinulata (Naudin) Bakh.f. which is also distributed in Peninsular Malaysia but differs in lacking paired hair cushions at the base of the leaves abaxiallyly (present in M. echinulata) and only has one pair of lateral appendages at alternipetalous stamens (which are fimbriate in M. echinulata).
2.  reduces this species to a variety of D. annulata based on the similarity in the number and shape of the stamens. Dissochaeta griffithii differs from D. annulata by its distinct triangular calyx lobes (truncate in D. annulata) and hypanthium with dense simple eglandular bristle hairs (lacking or with scattered glandular bristle hairs in D. annulata).
Distribution. Java (West). Ecology and habitat. Primary montane forest or in edge of forest in open, 1200-2000 m elevation.
Distribution. Borneo. Ecology and habitat. Mixed dipterocarp forest or heath forest at 600-800 m elevation.
Distribution. Borneo. Ecology and habitat. Lowland mixed dipterocarp forest or heath forest at 45-150 m elevation.

Dissochaeta leprosa
Distribution. Sumatra, Java and Lesser Sunda Islands (Bali). Ecology and habitat. Primary or secondary montane forest, rarely near crater, at 1000-1700 m elevation. Vernacular names. Java: harendong cai (Sunda); kramas madu (Java). Note. Dissochaeta leprosa resembles D. intermedia, but differs in the larger hypanthium and distinctly triangular calyx lobe tips. Otherwise, D. leprosa has a more tomentose indumentum than D. intermedia. The similarity in shape of the alternipetalous stamens between both species made  regard D. leprosa as a variety of D. intermedia, but because of the differences in size and shape of the hypanthium, the calyx lobe tips and the alternipetalous stamens, it is considered to be a distinct species (Kartonegoro and Veldkamp 2010).
Distribution. Borneo (Mount Kinabalu). Ecology and habitat. Lower montane forest, in open places, at ca. 914 m elevation.
Note. The indumentum of D. macrosepala resembles D. densiflora, but the former species is different in the long, lanceolate calyx lobes.  considered both species as varieties of D. rostrata. Stapf and Green (1914) incorrectly noted that the species has four stamens, but it has 8 stamens like the other similar species.

Dissochaeta marumioides
Distribution. Sumatra (West). Ecology and habitat. Montane forest at ca. 1600 m elevation. Note. Dissochaeta marumioides is only known from the type from Mount Singgalang, West Sumatra. This species has a non-bristly indumentum on branchlets and leaves; though sparse bristles are present on the hypanthium and calyx lobes. The 4 lateral appendages of the alternipetalous stamens are exceptional, all other species in the genus having 2. The calyx lobes with rounded apex are similar to those of D. rostrata from Borneo, but the species differs in the shape of the bracts.  SAR n.v.).
Vernacular name. akar kemunting (Kapit). Note. A distinct species that resembles D. viminalis in the number and shape of the stamens, but differs in having dense prominent bristle hairs on the nodes, petioles, bracts and bracteoles. Known only from the type from Kapit Division, Sarawak. ( SAN n.v.).
Distribution. Borneo. Ecology and habitat. Primary or secondary forest, low montane forest, river banks in riparian forest at 80-1000 m elevation. Notes. 1. Dissochaeta pulchra is easily recognised by its thin, glabrous, ovate-suborbicular leaf blade with minutely serrulate margin; all other species have entire margins. The crest-like interpetiolar ridge is similar to D. stipularis and D. pubescens, but there are differences in shape and number of the fertile stamens. This species also has abaxi-  KLU n.v., L [L.2533495]!, SING n.v.).
Distribution. Borneo (Brunei and Sarawak). Ecology and habitat. Heath forest or mixed dipterocarp forest at 240-1000 m elevation.
Distribution. Java and Lesser Sunda Islands (Sumbawa). Ecology and habitat. Forest, secondary or depleted forest or edge of river at 500-1400 m elevation. Vernacular names. Java: harendong areuy, harendong bokor areuy, harendong gede (Sunda). Note. Dissochaeta decipiens, with only four fertile, alternipetalous stamens, is synonymised with D. vacillans, because it has a similar appearance due to the indumentum on the branchlets, leaves and inflorescences; moreover, the shape of the stamens and the appendages are also similar. hairs at the midrib and nerves. Inflorescences terminal and axillary, when terminal up to 12 cm long, many-flowered, when axillary ones up to 5.5 cm long, 3-9-flowered; main axis stellate-puberulous; primary axes up to 5 cm long with 2-4 nodes, secondary axes up to 2 cm long with 1-3 nodes, tertiary axes when developed up to 0.5 cm long with 1 node; bracts linear or elliptic, 3-6 × 3-4 mm, stellate-puberulous, caducous; bracteoles ovate to oblong, 3-4 mm long, stellate-puberulous, margin ciliate; pedicels glabrescent