Dysoxylum
Description
Trees or shrubs, often very pachycaul, dioecious, more rarely with hermaphrodite flowers Indumentum of simple hairs, very rarely with stellate ones.
Leaves spirally arranged, rarely opposite, pinnate, occasionally with tardily developed apical leaflets, very rarely with winged rachis.
Inflorescences thyrses to racemose or spicate, sometimes reduced to fascicles or solitary flowers, axillary, ramiflorous or cauliflorous, sometimes with conspicuous bracteoles and these sometimes transitional to separate sepals.
Petals 3–6, free or adnate to base of staminal tube.
Staminal tube cylindrical to urceolate, margin entire, lobed or tipped with 6–10(–13) appendages; anthers 6–16, within throat of tube, pollen sometimes shed in tetrads.
Ovary 2–6-locular, each locule with 1 or 2 seeds; stylehead capitate to discoid.
Fruit a 2–6-valved capsule, each valve with 1 or 2 seeds.
Seeds anatropous, usually with aril or sarcotesta.
Distribution
Asia-Tropical: New Guinea present, Lord Howe Is present, New Caledonia present, New Zealand present, Norfolk Is present, Pacific: Fiji (Fiji present), east to Niue present, from India and Sri Lanka to S China present, throughout Malesia (including Christmas Island , 1) to the Pacific south to Australia present
About 80 species of tropical E Asia from India and Sri Lanka to S China(3), Indochina, throughout throughout Malesia (including Christmas Island , 1) to the Pacific south to Australia (14), New Caledonia (9), Norfolk Is. (1), Lord Howe Is. (1, endemic),New Zealand (1, endemic) and east to Niue (1).
Dysoxylum shows the greatest distribution of any Indopacific genus in the family with high levels of endemism in New Guinea (16 of 28; cf. Borneo with 2 of 22, Malay Peninsula with 2 of 17), Fiji (7 of 9) and New Caledonia (8 of 9), demonstrating a distinctly austral richness by comparison with its ally Chisocheton (Guareeae) and the other large genus in Malesia, Aglaia (Aglaieae). Unlike those then, Dysoxylum cannot be said to be essentially Malesian and has to be understood in a Pacific context.
Dysoxylum shows the greatest distribution of any Indopacific genus in the family with high levels of endemism in New Guinea (16 of 28; cf. Borneo with 2 of 22, Malay Peninsula with 2 of 17), Fiji (7 of 9) and New Caledonia (8 of 9), demonstrating a distinctly austral richness by comparison with its ally Chisocheton (Guareeae) and the other large genus in Malesia, Aglaia (Aglaieae). Unlike those then, Dysoxylum cannot be said to be essentially Malesian and has to be understood in a Pacific context.
Morphology
Dysoxylum differs from Chisocheton in its anatropous seeds. Otherwise there are great similarities in those species of Chisocheton with a prominent disk and no pseudogemmula, notably those in sect. Clemensia, where there are fruits with stinging hairs similar to those in D. sessile for instance.
Certain species, formerly excluded as the genus Didymocheton are notable for their spirally arranged sepals transitional to bracteoles. Spirals are otherwise found in meliaceous flowers only in certain species of sect. Holopentas of Chisocheton where the corolla may appear to have 2 whorls (the formerly segregated genus Megaphyllaea), though species with transitional forms link that to 1-whorled ones. The species with separate sepals are closely allied to the austral taxa in the genus, notably the species of New Caledonia and New Zealand. It is also notable that the most pachycaul species, D. sessile of the Moluccas has such a calyx. Sect. Cyrtochiton, by contrast, is poorly distributed outside Indomalesia.
For a summary of the limonoids in the genus and their biological activity, see
The range of form from pachycaul to leptocaul is mirrored in both Aglaia and Chisocheton, though the range of structure of the flowers and leaves is much greater in Dysoxylum than in Aglaia, where, however, fruit form is more varied.
Taxonomy
Dysoxylum sect. Cyrtochiton is marked by spike-like apical buds, 4- merous uniform flowers, usually in spicate inflorescences and (?) sarcotestal seeds with green cotyledons. The only examples of opposite leaves in the family are here, too. Dysoxylum cyrtobotryum in this group is replaced by D. latifolium to the east and this in turn by allied taxa in the western Pacific, while, to the west, there are other vicariant taxa.
A similar pattern is seen in the D. cauliflorum group, with D. cauliforum in Sumatra, the Malay Peninsula and Borneo, D. cumingianum largely in the Philippines and D. pettigrewianum in New Guinea and tropical Australia, and also in sect. Cyrtochiton with D. grande from continental Asia to Borneo, D. oppositifolium in the Philippines to Queensland, as well as D. rugulosum and D. brachybotrys west of Wallace’s Line, D. enantiophyllum in New Guinea. D. pachyrhache in Borneo and D. kaniense in New Guinea are a similar pair, as are D. magnificum and D. brassii (sect. Dysoxylum). Yet another pair with similar distribution relationships in sect. Dysoxylum is D. crassum (Borneo) and D. inopinatum (New Guinea).
In D. mollissimum (sect. Dysoxylum) the variation pattern is best represented as subspecific taxa either side of Wallace’s Line, the second being more or less Malesian, the first extending far into continental Asia on the one hand, to the western Pacific on the other.
The complex species D. excelsum and D. alliaceum are very variable and closely allied to one another, though they appear to have more or less distinct ‘satellite’ taxa, D. klanderi F. Muell. in Queensland, D. hongkongense (Tutcher) Merr. in China outside Malesia. Some of the most widespread species, D. arborescens, D. parasiticum and D. gaudichaudianum, seem rather uniform by comparison.
By contrast, some species are very restricted. The rheophyte D. angustifolium is found (only in the Pahang basin of the Malay Peninsula. Unlike this species or species in other genera that are restricted to e.g. peatswamp forests (Sandoricum beccarianum, Chisocheton amabilis), riparian forest (Sandoricum borneense), or ultramafic rocks (Walsura monophylla), others have no obvious ecological restrictions, e.g. D. boridianum from the village of Boridi, New Guinea.
The distinction between Dysoxylum and Guarea (Neotropics and Africa) is rather weak. The disk alleged to separate the two, in being characteristic of Dysoxylum, is scarcely formed in certain Dysoxylum species. Both genera are separable from Chisocheton in that the latter is marked by its orthotropous, rather than (hemi-)anatropous, seeds; many Guarea species have the pseudogemmula typical of Chisocheton species. The whole group is closely interrelated and the peripheral genera are very closely allied too, Anthocarapa Pierre (q.v.) being particularly weakly differentiated from Dysoxylum.
A similar pattern is seen in the D. cauliflorum group, with D. cauliforum in Sumatra, the Malay Peninsula and Borneo, D. cumingianum largely in the Philippines and D. pettigrewianum in New Guinea and tropical Australia, and also in sect. Cyrtochiton with D. grande from continental Asia to Borneo, D. oppositifolium in the Philippines to Queensland, as well as D. rugulosum and D. brachybotrys west of Wallace’s Line, D. enantiophyllum in New Guinea. D. pachyrhache in Borneo and D. kaniense in New Guinea are a similar pair, as are D. magnificum and D. brassii (sect. Dysoxylum). Yet another pair with similar distribution relationships in sect. Dysoxylum is D. crassum (Borneo) and D. inopinatum (New Guinea).
In D. mollissimum (sect. Dysoxylum) the variation pattern is best represented as subspecific taxa either side of Wallace’s Line, the second being more or less Malesian, the first extending far into continental Asia on the one hand, to the western Pacific on the other.
The complex species D. excelsum and D. alliaceum are very variable and closely allied to one another, though they appear to have more or less distinct ‘satellite’ taxa, D. klanderi F. Muell. in Queensland, D. hongkongense (Tutcher) Merr. in China outside Malesia. Some of the most widespread species, D. arborescens, D. parasiticum and D. gaudichaudianum, seem rather uniform by comparison.
By contrast, some species are very restricted. The rheophyte D. angustifolium is found (only in the Pahang basin of the Malay Peninsula. Unlike this species or species in other genera that are restricted to e.g. peatswamp forests (Sandoricum beccarianum, Chisocheton amabilis), riparian forest (Sandoricum borneense), or ultramafic rocks (Walsura monophylla), others have no obvious ecological restrictions, e.g. D. boridianum from the village of Boridi, New Guinea.
The distinction between Dysoxylum and Guarea (Neotropics and Africa) is rather weak. The disk alleged to separate the two, in being characteristic of Dysoxylum, is scarcely formed in certain Dysoxylum species. Both genera are separable from Chisocheton in that the latter is marked by its orthotropous, rather than (hemi-)anatropous, seeds; many Guarea species have the pseudogemmula typical of Chisocheton species. The whole group is closely interrelated and the peripheral genera are very closely allied too, Anthocarapa Pierre (q.v.) being particularly weakly differentiated from Dysoxylum.
Citation
A. Juss. 1832 – In: Mém. Mus. Nat. Hist. Nat. Paris: 227.
T.D. Penn. 1975: p. 502. – In: Blumea: f. 13d
Mabb. 1989: p. 239. – In: Tree Fl. Malaya: f. 6.
Large & Mabb. 1994 – In: Bot. J. Linn. Soc.: 1.
T.D. Penn. 1975: p. 504. – In: Blumea: f. 14a–d, excl. syn. Harpagonia Noronha (=Psychotria L., Rubiaceae)
Harms 1940: p. 167. – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl: t. 35 f. K, N–Q.
Mabb. 1988 – In: Fl. Nouv.-Caléd. et Dép: 23
Harms 1940: p. 160. – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl: t. 35 f. F–J
Harms 1940 – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl: 139
Harms 1940: p. 156. – In: Engl. & Prantl, Nat. Pflanzenfam., ed. 2, 19bl: t. 35 f. L, M.