A Key to Rhacocarpaceae of the world

Jan-Peter Frahm

Extracted from: Cryptogamie, Bryologie. Lichénologie 17(1):39-65 (1996)

Translated by B.J. O'Shea

There is only one genus, Rhacocarpus, in this family.

(NB African species of Rhachocarpus are dealt with in more detail below.)

1	Leaf ending in a definite hairpoint	2
1*	Leaves not ending in a long hairpoint. Leaf point lanceolate or apiculate	6

2	Leaf margin without border	*R. chlorotus*
2*	Leaf at least partly bordered	3

3	Leaf margin bordered throughout length	*R. purpurascens*
3*	Leaf with margin only in lower part	4

4	Leaf point (at least on the stem leaves) with notches at the base of the hairpoint	*R. excisus*
4*	Leaf point without notches	5

5	Leaf alar cells collenchymatous, thickened. Upper leaf margin toothed (Australia)	*R. rehmannianus* var. *webbianus*
5*	Leaf alar cells not collenchymatous and thickened. Upper leaf margin smooth (Brazil)	*R. inermis* var. *piliformis*

6	Leaf point apiculate	7
6*	Leaf point lanceolate or with short point	*R. inermis* var. *inermis*

7	Leaves panduriform. Upper laminal cells elongate	8
7*	Leaves not panduriform. Upper leaf cells oval	*R. rehmannianus* var. *rehmannianus*

8	Upper leaf margin toothed. Leaf border extended into the point	9
8*	Upper leaf margin smooth or finely toothed. Leaf border 2/3 - 3/4 of leaf length	*R. inermis* var. *cuspidatulus*

9	Leaf suddenly contracted into an apiculus (Andes)	*R. apiculatus*
9*	Leaf gradually acuminate (SE Asia)	*R. alpinus*

TBG45/rhaco Issue 1 - 12.01.97

A Key to African Rhacocarpaceae

Extract from: O'Shea, B.J. 1997. British Bryological Society Expedition to Mulanje Mountain, Malawi. 9. Regmatodontaceae, Rhachitheciaceae, Rhacocarpaceae and Rhizogoniaceae (Bryopsida). Journal of Bryology 19(4)

The family Rhacocarpaceae Kindb. was synonymised with Hedwigiaceae Schimp. for many years, until Buck & Vitt (1986) resurrected the original family name, being convinced that the only genus Rhacocarpus was misplaced in Hedwigiaceae. De Luna's (1992) work on the Hedwigiaceae also produced convincing evidence that it was unrelated to that family. Buck (1995) redescribed the genus and reviewed the evidence in some detail and concluded that it was acrocarpous, and that the family was probably related to Dicnemonaceae in the Dicranales.

This confusion becomes understandable on seeing members of the family. The plants are well-grown and characterised by erect or prostrate, well-branched, rigid stems with cuspidate apices. Particularly when dry, the plants have a glossy, gold-red-bronzed appearance. Under the hand lens, the leaves are thick and opaque and African plants have distinct, abruptly-narrowed apices with hairpoints. Under the microscope, the leaves are panduriform and can be seen to have a surface covered with a multi-layered, reticulate structure, through which the internal structure of the leaf can be seen.

The leaves are very variable in structure and appearance, particularly in the most widespread species, Rhacocarpus purpurascens (Brid.) C. Müll., which over the years led to the description of many spurious taxa. The number of species in the genus is now reduced to seven, following a revision of the genus by Frahm (1995). The genus is tropical/Southern Hemisphere in distribution, with four species in America, one in Malesia, one in both South Africa and western Australia, and one occurring throughout the area.

Key to African species of Rhacocarpus

Leaves with hairpoint, border full length of leaf	R. purpurascens
Leaves apiculate, border for only ½ to ¾ of leaf	R. rehmannianus var. rehmannianus

Rhacocarpus rehmannianus var. rehmannianus is known only from Cape Province, South Africa, and Lesotho; R. purpurascens is pantropical/subtropical.

Frahm (1995) produced a mainly synoptic treatment, without descriptions of the taxa, but with a key to all the world's taxa (see above). It also contains leaf-shape illustrations of the taxa, and leaf surface scanning electon micrographs for some. A description and illustration of Rhacocarpus purpurascens (Brid.) C.Müll. (R. purpurascens var. rufipilus (Ren. & Card.) Wijk & Marg.) can be found in Koponen & Norris (1986).

References
Buck WR. 1995. The systematic position of the moss genus Rhacocarpus. Fragmenta Floristica et Geobotanica 40: 127-131.
Buck WR, Vitt DH. 1986. Suggestions for a new familial classification of pleurocarpous mosses. Taxon 35: 21-60.
De Luna E. 1992. Developmental and systematic studies in the Hedwigiaceae (Musci). Duke University, Ph.D. dissertation, 216pp. Ann Arbor: University Microfilm International.
Frahm J-P. 1995. Revision der Gattung Rhacocarpus Lindb. (Musci). Cryptogamie, Bryologie. Lichénologie. 17: 39-65.
Koponen T, Norris DH. 1986. Bryophyte flora of the Huon Peninsula, Papua New Guinea. XVII. Grimmiaceae, Racopilaceae and Hedwigiaceae (Musci). Acta Botanica Fennica 133: 1-24.