Re-shaping mallotus [ paRt 2 ] : inclusion of neotRewia , octospeRmum and tRewia in mallotus s . s . ( euphoRbiaceae s . s . )

A recent molecular phylogenetic study of Mallotus and related genera showed that three small Asiatic genera are clearly part of a strongly supported main Mallotus clade (Mallotus s.s. clade), rendering the genus paraphyletic. In this paper these genera, Neotrewia, Octospermum and Trewia, are merged with Mallotus. The monotypic Neotrewia and Octospermum were originally described within Mallotus and are now transferred back to it. Trewia was never included in Mallotus; it has two distinct species, for which new combinations within Mallotus are made. A full taxonomic treatment with descriptions, distribution maps and drawings is given for the species transferred, and a new generic description for Mallotus is provided. The morphology of the newly transferred species in comparison to Mallotus in general and to related species in particular is discussed.

already merged with Mallotus (Airy Shaw, 1963;Bollendorff et al., 2000).In this paper Neotrewia, Octospermum and Trewia, three Asiatic mono-or ditypic genera largely resembling Mallotus, are merged with it and a new circumscription of Mallotus s.s. is provided.The morphology of the four transferred species is discussed in comparison to Mallotus and a taxonomic treatment of them is given with morphological descriptions, distribution maps and drawings.

MORPHOLOGICAL COMPARISONS
Mallotus and the species previously assigned to Neotrewia, Octospermum and Trewia have a very similar general appearance.In particular, they share the pollen type (perforate/microreticulate ornamentation with scabrae) and the extrafloral nectaries on the upper leaf surface.Furthermore, all these taxa possess a similar type of glandular hairs 1 , a character typical for most Mallotus and Macaranga species and rare outside subtribe Rottlerinae (Macaranga is a sister clade of the Mallotus s.s.clade; see Kulju et al., in press).The morphological similarity of Neotrewia and Octospermum with Mallotus is additionally demonstrated by the fact that they are solely based on species originally described within Mallotus.Also, at least in the cases of Octospermum and Trewia, Mallotus species or species groups clearly similar to them can be found (see below); this bridges further the gap between the genera.
In fact, the only characters distinguishing Neotrewia, Octospermum and Trewia from Mallotus are the number of locules in the ovary and the fruit type.The locule number in these genera can vary from one to nine (2-or 3-locular ovaries are typical for Mallotus) and the fruits are indehiscent 2 (generally dehiscent in Mallotus).These differences, especially the fruit dehiscence, are of course distinct and easily notable, but they form a weak justification for a separate generic status, because the variation in these characters within Mallotus is larger than generally acknowledged.Firstly, some Mallotus species can have up to five locules per ovule (Sierra & Van Welzen, 2005;Sierra et al., 2005).Secondly, indehiscent fruits are present in several Mallotus species (e.g., M. blumeanus Müll.Arg., M. chromocarpus Airy Shaw and M. sphaerocarpus Müll. Arg.; also several species formerly assigned to the genus Coccoceras have indehiscent or tardily dehiscent fruits; Bollendorff et al., 2000).The development of indehiscent, often fleshy, fruits from typical explosively dehiscent euphorb capsules seems to have independently happened in several Euphorbiaceae groups (Haegens, 2000;Esser, 2003;Wurdack et al., 2005), leading to paraphyletic taxa if this transformation is given too much weight, as demonstrated in this case.

Neotrewia
The monotypic Malesian genus Neotrewia was described by Pax & Hoffmann (1914), based on Mallotus cumingii Müll.Arg., a name which is adopted here again.The same species was also described as Trewia ambigua by Merrill (1906).The fruits of this species are unilocular (or rarely bilocular) and indehiscent.The pericarp wall is apparently not fleshy.The opposite leaf arrangement suggests affinity with the species-rich section Rottleropsis of Mallotus (see the revision by Sierra et al., 2007); this is confirmed by the phylogenetic study (Kulju et al., in press).

Octospermum
Pax & Hoffmann (1914) described Mallotus pleiogynus, a new species of Mallotus from New Guinea and placed it in the new and monotypic section Pleiogyni.Because of its peculiar pistillate characters, Airy Shaw (1965) transferred it to the new genus Octospermum.This species has 7-9-locular ovaries and toughly fleshy, indehiscent fruits with longitudinal ridges.It is also an exceptionally tall tree (up to 43 m) as compared to other Mallotus species.
However, M. pleiogynus has similarities with three other Mallotus species from New Guinea and Australia (M. chromocarpus Airy Shaw, M. discolor F. Muell.ex Benth. and M. nesophilus Müll.Arg.):stipules absent, anther connectives conspicuously broadened (umbrella-like) and fruits indehiscent.In the phylogenetic study M. pleiogynus groups with M. discolor (the other two species were not sampled).A tentative sister species to M. pleiogynus is M. chromocarpus, another New Guinean endemic (the two other species in this group are Australian), as they differ primarily by the number of locules (3-5 in M. chromocarpus; Sierra et al., 2005).All of these four species have alternate leaves and unarmed fruits, a combination typical for Mallotus sect.Philippinenses. However, Sierra et al. (2005) excluded M. chromocarpus from this section based on the special characters mentioned above (the same applies to M. discolor and M. nesophilus).Due to poor support in the phylogenetic tree (Kulju et al., in press), this could not be verified, although sect.Philippinenses, with or without the four species mentioned here, does not seem to form a monophyletic group.

Trewia
Trewia was established by Linnaeus (1753) based on the single species T. nudiflora.The description of this species is solely based on the figure of 'Canschi' in Van Rheede's Hortus Malabaricus (1678).Willdenow (1797) described the same plant as Rottlera indica, but later synonymised it with T. nudiflora (1806).He (1797) also treated Tetragastris ossea Gaertn., the type species of Tetragastris Gaertn., as a synonym of R. indica.This makes the name Rottlera indica superfluous and, actually, a synonym of the genus Tetragastris in the Burseraceae (Tetragastris ossea has been shown to belong to the Burseraceae and be related to the genus Protium; see Swart, 1942).
Several Trewia species were described after Linnaeus, but most of these proved either to be conspecific with T. nudiflora or to belong to other Euphorbiaceae genera.Only the status of the Indian T. polycarpa Benth.raises serious taxonomic questions (see below).
In the phylogenetic tree (Kulju et al., in press) T. nudiflora forms a highly supported clade with Mallotus khasianus Hook.f. (sect. Rottleropsis;Sierra et al., 2007); both have an often deciduous habit and similar, long staminate inflorescences.As this clade is positioned as sister to the rest of Mallotus s.s., Mallotus could be made monophyletic by transferring M. khasianus to Trewia.However, we opt for an alternative solution, which is to merge T. nudiflora with Mallotus, for two reasons.First, the sister group relationship of the T. nudiflora-M.khasianus clade and the rest of Mallotus s.s. is not well supported (also, the preliminary analyses with different markers and more extensive taxon sampling place this clade nested inside Mallotus s.s.).Second, M. khasianus has typical dry, dehiscent Mallotus capsules, and merging it to Trewia would leave both genera without a distinguishing set of morphological characters.Therefore, a new combination for T. nudiflora, Mallotus nudiflorus (L.) Kulju & Welzen, is made here.
Trewia, a Linnaean name, is older than the name Mallotus and, therefore, all Mallotus species should be transferred to Trewia.However, this would cause a great nomenclatural instability, requiring new combinations for more than a hundred Mallotus species.Mallotus is far more widely known than Trewia, not only because of the many species, but also because it has a much wider distribution, ranging from Africa to the West Pacific.Furthermore, Mallotus is not only a name familiar among systematists, it is an ecologically important genus too; Mallotus species are, for instance, important as ecological indicators (Slik et al., 2003;Slik, 2005).As a transition of Mallotus to Trewia is thus unwanted, we have submitted a proposal to conserve the genus Mallotus against Trewia (Kulju & Van Welzen, submitted), and in the present paper the name Mallotus is used for the genus.

The intraspecific variation of Mallotus nudiflorus
Mallotus nudiflorus, having a relatively wide distribution range from India to West Malesia, shows considerable variation in the type and density of the indumentum, the number of fruits per pistillate inflorescence and the size of the fruit.The indumentum varies from dense with long hairs to subglabrous with short hairs.This variation is seemingly uncorrelated with geography, because the different forms occur within most areas (Table 1).Variation in the fruit size is mainly caused by the thickness of the pericarp and is loosely correlated with the number of fruits per infructescence (1-or 2-fruited infructescences tend to have bigger fruits than many-fruited ones).Overall, M. nudiflorus is most diverse in India.

The status of Trewia polycarpa
Bentham & Hooker (1880) distinguished the Indian species T. polycarpa from T. nudiflora by several pistillate characters, and various Indian floras have followed After studying the Indian material previously known as Trewia, including the type of T. polycarpa, we conclude that M. polycarpus is indeed a separate species from M. nudiflorus because of the strong differences in inflorescence and fruit (compare Fig. 2 and 4).Mallotus nudiflorus has 1-5-flowered pistillate inflorescences with flowers only in the apical part, 3-5-locular ovaries and indehiscent, oblate fruits; whereas M. polycarpus has 6-17-flowered pistillate inflorescences with flowers also in the basal part, 2-locular ovaries and loculicidally dehiscent, ovoid to ellipsoid fruits.
The above-mentioned differences are consistent with the original diagnosis of T. polycarpa, in which, however, Bentham & Hooker (1880) also referred to two previously published figures of pistillate specimens as T. polycarpa.These figures (Wight, 1852(Wight, : t. 1871;;Beddome, 1872: t. 281) have a 3-or 4-locular ovary and M. nudifloruslike inflorescences and, therefore, clearly represent M. nudiflorus as delimited here.The presence of these two conflicting elements in Bentham & Hooker (1880), the diagnosis (matching the type) and the figure references (resembling M. nudiflora), was probably the original source of the confusion concerning the status of these two taxa in many Indian floras and the tendency to treat the two species as synonyms.
Indian Trewia material studied here (c.90 specimens) contained only two true M. polycarpus specimens with 2-locular, dehiscent fruits (although several collections of M. nudiflorus were misidentified as it).A search through Indian Mallotus material at L and K did not reveal additional M. polycarpus specimens either.Apparently, this species is very rare.
Because DNA extractions from M. polycarpus were not successful, it was not included in the phylogenetic study (Kulju et al., in press).Although a plant with globose to discoid glandular hairs, extrafloral nectaries on the upper leaf surface and 2-locular ovaries could be placed in the genus Macaranga as well, the presence of opposite leaves, unequal in size, clearly point to Mallotus s.s.However, because of the strikingly different inflorescence and fruit and the scarcity of material, especially the absence of staminate specimens, it is unclear if this species could be the sister species of M. nudiflorus or if it is more closely related to other Mallotus species.Notes -1.Trewia L. is the oldest name for the genus, as circumscribed here.However, we have submitted a proposal to conserve Mallotus against Trewia to maintain nomenclatural stability (see text).
2. Originally Linnaeus (1753) spelled the genus name as 'Trevia', but later he inconsistently used both 'Trevia' and 'Trewia' (see Nicolson et al., 1988).Since Linnaeus, almost all authors have adopted the spelling 'Trewia'.The present code (McNeill et al., 2006: art. 13.4) gives priority to the original spelling given in Species Plantarum (1753) and therefore 'Trevia' should be used.However, since this genus is here present only in the synonymy of Mallotus, we have continued to follow the widely used spelling 'Trewia'.Shrubs to small trees up to 18(-25) m high, dbh up to 30(-45) cm, dioecious, evergreen; young branches usually flattened when dry, sparsely to densely hairy, older ones terete, glabrescent; flowering branches 1-5 mm thick.Outer bark smooth to rugose, often peeling in thin plates, grey to (yellowish or reddish) brown, sometimes patchy.
Habitat & Ecology -In primary and secondary forest, frequently in damp places along rivers and streams.Altitude up to 1000(-1660) m.Flowering and fruiting (in Philippines): throughout the year, flowering especially from March to June.
Notes -1.This species shows a large variation in leaf size, which is partly caused by the size inequality of each leaf pair.The variation is, however, continuous and does not correlate with other characters.Specimens from Batan Island, Philippines (BS 80605, BS 80686, BS 80720) differ from others by having only ovate leaves with low length/width ratios and somewhat longer staminate bracts.
2. The distribution of this species, previously only know from the Philippines and Sulawesi, is here extended to Borneo.Only one Bornean specimen, S series 28705 (Kapit Distr., Sarawak), is known so far.
Africa to West Madagascar, Pakistan, Sri Lanka, India, Bangladesh, Myanmar and Nepal, South China, Korea, South Japan, throughout Southeast Asia and Malesia to East Australia and the West Pacific (Solomon Islands, Palau, Federated States of Micronesia, New Caledonia, Fiji).
distinct longitudinal ridges when dry, surface somewhat irregulary wrinkled, covered with glandular hairs, yellow to orange when fresh, yellowish to reddish brown with dark grey ground colour when dry; pericarp toughly fleshy, hard when dry. Seeds radially arranged; obloid, somewhat flattened, 5.2-5.6 by 6.2-6.8 mm, surface slightly rugose, brown to light brown, shiny, sarcotesta absent.