Phylogenetic studies based on DNA sequence data have culminated in the treatment of Crepidium and related genera in Genera Orchidacearum vol. 4 (Pridgeon et al., 2005). According to this treatment the name Malaxis should be reserved for a group of species occurring in part of the neotropics as well as in continental Asia, Africa, Europe and North America. It would appear that these species all have not-plicate leaves. All Malesian species including the New Guinea species have plicate leaves and should be assigned to the genus Crepidium, with the exception of Malaxis ophrydis, which should be called Dienia ophrydis. We consider that more work is needed to fix the generic boundaries and to establish morphological support for the clades found in molecular studies.
Members of the genus Crepidium (until recently known as Malaxis) are small, soft-leaved plants, usually growing in moist shady spots on the forest floor, with plicate leaves and slender racemes with usually quite inconspicuous greenish or purplish flowers. The flowers are not resupinate. Crepidium is not common in cultivation, but several species would be well worth growing for their nicely coloured foliage, which may be e.g. bluish green with light brown bands, ochrish brown, or glossy purple. Most species have plain green leaves, however. In some species of section Pseudoliparis the column is almost indigo-blue.
Schlechter (1911-1914) has proposed an infrageneric classification for the New Guinea species of Crepidium (or rather Microstylis, as he called this genus). The comments we made under Liparis (Schuiteman & de Vogel, E.F. 2006.) apply here as well, in that these sections may not always conform to true clades, but that they are useful for identification purposes. Mainly for this reason we have retained Schlechter's classification, with some modifications.
There have been various proposals to split up genus Malaxis (now Crepidium) into several smaller genera, notably by Szlachetko and his collaborators. In this view the New Guinea species of Crepidium should be distributed over the following genera: Crepidium, Dienia, Fingardia, Pseudoliparis and Saurolophorkis. However, these proposals are not backed by phylogenetic analyses and, in our opinion, they are highly subjective, so we have decided not to follow them.
Ormerod (2017) maintains 2 subgenera in Crepidium : Crepidium and Pseudoliparis (Finet) Szlach. Since we have not evaluated the justification of these subgenera we for now refrain from using them, but we do follow his subdivision in sections, with some slight deviations.
We find it difficult to keep the sections Commelinodes and Crepidium (syn. Microstylis sect. Pleiodon Schltr.) separate (Schuiteman & de Vogel, E.F. 2006.) . According to Schlechter, members of sect. Commelinodes should have elongated, decumbent and rooting stems, while sect. Crepidium should have short, crowded and erect stems that root only at the base. The flower structure, as Schlechter himself already noted, is identical in the two sections. But the vegetative differences are not at all as clear-cut as Schlechter implied. There are several species for which it would be quite arbitrary to assign them to one section or the other. For example,Crepidium vinicolor was included by Schlechter in section Crepidium (Pleiodon as Schlechter called it). As can be seen from the photograph of a type specimen (448-318T.JPG ) this species has quite elongated rhizomes, and except for the lower number of leaves there is no essential difference with a species like Crepidium fissum (448-83U.JPG ), which Schlechter included in section Commelinodes. Seidenfaden (1978) maintains the distinction between the sections Commelinodes and Crepidium and suggests as an additional difference that the stems in sect. Commelinodes are not swollen, while in sect. Crepidium they are often swollen into pseudobulbs. Having seen living specimens of many species of genus Crepidium we have to disagree with the statement that the stem in sect. Commelinodes is never swollen. Ormerod (2017) also maintains the two sections, adding as an addituonal character laxly positioned leaves in Commelinodes versus leaves clustered together in section Crepidium. Summarising, we think that for the New Guinea members of the genus Crepidium the distinction between sections Commelinodes and Crepidium can not be upheld in a revision of the complex. This was apparently also the position of J. J. Smith, since he included 'typical' species of sect. Commelinodes in sect. Crepidium. We agree with Ormerod (2017) that sect. Herpetorhizis, which is characterised by the shoots appearing at long intervals along a creeping rhizome, should be included in sect. Crepidium.
Finally, we consider that section Ophthalmodes is not well separable from sect. Holobos, since Malaxis carinatifolia (J.J.Sm.) P.F.Hunt could be accommodated in both. A key to the sections is found below.
KEY TO THE NEW GUINEA SECTIONS OF GENUS CREPIDIUM
adapted to the characters mentioned in Ormerod (2017)
1a. Lip in the apical part with denticulate margins or with 4 or more teeth or filaments == 2
1b. Lip in the apical part entire or 2- or 3-lobulate == 3
2a. Rhizome either very short or elongated, distinctly demarcated from the usually basally swollen stem with clustered leaves == sect. Crepidium (syn. sect. Pleiodon Schltr. and sect. Herpetorhizis Schltr.)
2b. Rhizome long, creeping, leafless, gradually passing in the laxly leaved shoot == sect. Commelinodes Schltr.
3a. Lip in front 3-lobed, without basal auricles == sect. Gastroglottis (Blume) Ormerod (syn. genus Dienia)
3b. Lip in front entire or very indistinctly 3-lobed, with basal lobes (auricles) that are more or less clasping the column == 4
4a. Front margin of lip not 3-lobed, without teeth, often with a bilobulate tip. Column not elongated, without apical wings == sect. Hololobos (Schltr.) Margonska (syn. sect. Bothrocardia Schltr, sect. Ophthalmodes Schltr.)
4b. Front margin of lip entire or very indistinctly 3-lobed, the apex not bilobulate. Column often somewhat elongated, with large, often decurved apical wings or arms, often with a horn-like dorsal projection == sect. Oistochilus (syn. sect. Pseudoliparis)
Genus Crepidium in New Guinea contains c. 104 species and 6 varieties:
Crepidium fasciatum var. concolor
Crepidium nitidum var. cyclopensis
Crepidium oliganthum var. neuroglossum
Crepidium retusum var. brevis
Crepidium sciaphilum var. bismarckiensis
Crepidium warianum var. oreogenum