Notes

Xysmalobium as hitherto defined is very ambiguous in character, and by the definitions given cannot be distinguished from Asclepias and Schizoglossum. Originally it was separated from Asclepias by R. Brown to include those species which have 5 minute lobules or teeth alternating with the 5 coronal-lobes, without giving importance to other characters. R. Brown only refers two species to it, viz., Asclepias undulata, Linn., and A. grandiflora, Linn. f., two plants, which according to modern views, cannot well be placed in the same genus. The minute alternating lobules, although of specific value, are not of generic importance, since they are present in Xysmalobium decipiens, N. E. Br., and absent in the closely allied X. Holubii, Scott-Elliot. In Asclepias also there are some species with, others without them. Bentham & Hooker distinguish Xysmalobium by the following character, “coronal-scales flat, unappendaged,” but this character neither applies to all the species of Xysmalobium, nor distinguishes it from Schizoglossum. This absence of a definite distinguishing character has led to much confusion during recent years; even the same species is referred to another genus by the same or a different author. Undoubtedly Xysmalobium, Asclepias, and Schizoglossum are but artificial divisions of one natural genus, since they cannot be separated by characters that do not break down at some point, yet as there are 3 types of coronal structure in the group, it seems undesirable to follow Baillon, who in his “Histoire des Plantes,” x. 226, unites them, or Schlechter, who in the “Journal of Botany,” 1896, 451 (without assigning reasons), unites Xysmalobium with Asclepias, retains Schizo-glossum and refers some species, which I cannot separate from Xysmalobium, to other genera. Therefore in dealing with the Tropical African species of this group I have sorted them as follows: All species in which the coronal-lobes are cucullate or more or less complicate or cleft on the inner face, are laterally compressed or at least measure as much from front to back as they do in breadth, with or without a horn or other process in the cavity, and are never dorsally flattened, I refer to ASCLEPIAS. All species in which the coronal-lobes are dorsally flattened, or if concave or with incurved edges, then always broader than they measure from front to back, usually with 2 slight or wing-like parallel keels and with or without 1 or more horns or other appendages on the inner face, and are never laterally compressed, cucullate or complicate, or with a single median keel, I refer to SCHIZOGLOSSUM. All species in which the coronal-lobes are very thick or laterally compressed, with or without teeth or keels on their inner face, or, if dorsally flattened, are still comparatively thick and entirely without keels or have only 1 rather stout longitudinal median keel, but no filiform horn or tongue-like process on the inner face, solid, never cucullate complicate or cleft down the inner face, I refer to XYSMALOBIUM. Kanahia, which is also allied, and in coronal structure contains species referable to both Xysmalobium and Asclepias, may be retained as distinct from both by its inflorescence.