The species of Alangium section Rhytidandra ( Alangiaceae )

Alangium sect. Rhytidandra is confined to SE Asia, the Pacific and East Australia, and contains 13 species. Five species, viz. Alangium brassii, A. glabrum, A. gracile, A. guadalcanalense, and A. velutinum are described as new, whereas A. villosum subsp. solomonense is raised to specific rank: A. solomonense. Subspecies tomentosum formerly in A. villosum is transferred to another species and has become A. polyosmoides subsp. tomentosum. Finally Iodes ferruginea, described in Icacinaceae appeared to belong in Alangiaceae, and as the name ferruginea was occupied in Alangium it is changed into A. strigosum, nom. nov. A key to the species is presented, and the concerned taxa are enumerated, referenced, described, and two are figured.


INTRODUCTION
There are four sections in the genus Alangium and the number of species occurring in Malesia is estimated at c. 38 (but there are some collections which cannot be placed, and wait for additional material to be described).The sections are: sect.Bloembergen (1939).The section comprises the group of species with stamens equal in number to petals and is furthermore defined by a deeply 2-lobed stigma and petals generally more or less connate at base.The section is distributed from Java eastwards into East Malesia, the Pacific and East Australia.
After deliberate consideration Bloembergen (1939: 201) decided to accept for the section only one single species, Alangium villosum Blume, with ten geographically separated subspecies and an eleventh undescribed subspecies of which at the time only sterile material was at hand.The present authors reconsidered the matter and, with much more material available than in 1939, accept thirteen species with one including two subspecies.Five species are here described as new, whereas one species needed a new name, A. strigosum (for Iodes ferruginea).Some of Bloembergen's subspecies are re-instated as species and one is raised to specific rank: Alangium solomonense.The above-mentioned 11th subspecies seen by Bloembergen (1939: 210)  The mode of venation, used as a character for species distinction, viz.lamina at base palminerved (or 3-plinerved) vs lamina entirely pinninerved is not always very clear.Leaves with weak basal veins may pass for entirely pinninerved.
The species of sect.Rhytidandra generally have domatia in (part of) the axils of the lateral nerves, or sometimes just glands close to the nerve axils.They seem to be absent in, for example, A. guadalcanalense and A. villosum.Some species in sect.Alangium also have domatia.
The basically cymose inflorescences in sect.Rhytidandra are here described as 'simple' or 'compound'.It denotes, as far as the limited material seen allows, a distinction which may be helpful in the definition of species.In a 'compound' cyme the peduncle continues above the (sub)opposite first lateral branches not with a single flower but reiterates in a more complex several-flowered central branch.This situation is prevalent also in, for example, A. griffithii of sect.Marlea.
In the present paper, all species of Alangium sect.Rhytidandra are enumerated, referenced and briefly annotated where appropriate.

KEY TO THE SPECIES OF ALANGIUM SECTION RHYTIDANDRA
The key presented here is largely based on flowering specimens.Although construction of a dichotomous key is impractical for fruiting specimens, most can nevertheless be identified with the help of fruit size and provenance, as follows: 2. As common in species of sect.Rhytidandra domatia are present in the axils of the lateral veins.In A. brassii, however, there are no real domatia but rather distinct round glands at some distance from the vein axils.
Distribution -The species is only known from the type.
Habitat & Ecology -In Nothofagus dominated rain forest; c. 2000 m altitude; flowering and fruiting in September.
Note -The fruiting pedicel is remarkably long, 5 -7 mm.Etymology.The species epithet 'gracile' refers to its slender peduncle and corolla in bud.
Distribution -Papua New Guinea (Eastern Highlands and Central Provinces).
Habitat & Ecology -Montane forest, stream side, scattered in forest; 1060 -2600 m altitude; flowering from September to December; fruiting from September to November.
Habitat & Ecology -Well drained primary forest, ridge top; c. 600 m altitude; flowering in June.
Field-notes -Bole straight but leaning; bark surface grey, smooth.
Habitat & Ecology -(Primary) forest; 15 -900 m altitude; flowering all year round but mostly in February; fruiting mostly in April and May.

Notes
Note -Alangium polyosmoides is a variable species, in which two taxa, apparently with some intermediates, can be recognised; we follow Bloembergen (1939) and Hewson (1984) in ranking them as subspecies.Habitat & Ecology -Well drained primary rain forest, on flat plain, ridge side and ridge top; brown sandy loam and coral; from sea level to 300 m altitude; flowering and fruiting all year round.

Key to the subspecies
Field-notes -Common in lowland rain forest; buttresses mostly absent.
Notes -1.Alangium solomonense resembles A. pilosum, the latter differs in a slightly smaller corolla, a glabrous style, and smaller fruit.
Notes -1.Alangium strigosum needed a new name, because it was previously described as Iodes ferruginea (in Icacinaceae) which cannot be combined in Alangium because of A. ferrugineum.
2. The lectotype, in WRSL, bears the number Lauterbach 387, but in the protologue the number is changed into Lauter bach 2387, presumably the number 2 is added to indicate that the collection was from 'Lager' = camp 2.
3. Alangium strigosum resembles A. velutinum, the latter is a montane species distinct in conspicuous dense red-brown indument.
4. The species is known from two collections: the type and Pullen 1810 (L), from Sepik Prov., Wewak-Angoram Area, c. 50 m alt., 1 Oct. 1959, fl.Etymology.The specific epithet 'velutinum' refers to the velvety surface of the lamina below.

DOUbTFUL COLLECTIONS
Five mutually different collections (all in L), one with fruit and 4 with flowers, obviously belong to the group of species around A. ferrugineum, but we cannot satisfactorily link them up with any of the accepted species.They cannot be described adequately as new species either by lack of flowers or of fruit, and one should wait for additional materials to be collected.Acknowledgements The materials necessary for the present study were basically those of herbarium collections in L (including U) of which most older collections were identified by the last monographer Bloembergen.In addition we thank the curators in BO, K, and SING for allowing us to study their collections and we thank Krzysztof Świerkosz (WRSL) for providing a photo of the holotype of Iodes ferruginea and Danielle Hanharan (A) for a photo of the isotype of A. warburgianum.The study in SING was made possible by a grant generously provided by the Singapore herbarium.The illustrations are as usual by the Leiden artist Jan van Os.
appeared, with the aid of subsequently collected fertile material, to belong to sect.Conostigma Bloemb.(see De Wilde & Duyfjes 2017) and has been recognised as a new variety of Alangium maliliense Bloemb.
Alangium sect.Rhytidandra was established by
-1. Plants from the Philippines are generally more densely and longer hairy (hairs 0.2-0.3mm long) as compared with those of Lesser Sunda Isl., with hairs c. 0.1 mm long or plant occasionally subglabrous.2. Two collections in L, from N Moluccas, Halmahera, viz.De Vogel 4419 (fl.) & 4452 (fr.) may represent a new species.They key out on A. pilosum, but they look quite different by having broader more densely hairy leaves.The specimens are stored under Alangium aff.pilosum.An eventual description should wait for additional fruiting material.