Studies in the Ericoideae. II. The new genus Stokoeanthus

The new monotypic genus Stokoeanthus is described, its type and only species being the new species S, chionophilus E. G. H. Oliver. The position of the genus in the subfamily, its relationships and the reasons for its establishment are given.

The unusual feature of the species is found in the ovary, which is 2-celled with usually 3 pendulous ovules per cell, rarely 2, 4, 5 or 6. This character is unique in the subfamily and does not occur to the author's present knowledge, in any other genus.
Of the 23 genera at present recognized in the Ericoi deae occurring in Southern Africa there are only a few which have more than 2 ovules per cell i.e. Erica, Blaeria, Thamnus, Ericinella, Philippia, Coccosperma, and Nagelocarpus. The last three genera possess no bracteoles, unequal calyces and connate stamens and therefore need not be considered in any relationship with the species under discussion.
In Ericinella the calyx is unequal and there are no bracteoles, but the stamens are free. This genus is of the philippioid type and, in addition, it is not part of the south-western Cape flora. Thamnus which occurs in the eastern Cape is similarly far removed from the south-western Cape. It is a unique monotypic genus having a 1-celled ovary with 4 pendulous ovules around a free central placenta.
Of the remaining two genera, Erica bears a close superficial resemblance to the new species. In fact, the new taxon could easily be mistaken for being a species of Erica. There are some Erica spp. which have as few as 1 and 2 ovules per cell in the ovary, especially those belonging to the section Euryloma, but none o f them has 2 cells. The vast m ajority of species in Erica have 8 stamens and only four species (0,75%) have been recorded with 4 stamens. These latter, however, have 4-celled ovaries. Thus the com bi nation o f 4 stamens and a 2-celled ovary serves to distinguish the new taxon from species o f Erica.
The possession of 4 stamens is, however, the only character, although somewhat tenuous, used to distinguish the genus Blaeria from Erica. This makes the relationship of the new taxon closer to Blaeria. But here again the ovary is at variance, as in Blaeria there are 4 cells in the ovary. The possibility o f the plant being a species of Blaeria with reduction in ovary parts was examined. This would mean an altera tion in the ovary characters for Blaeria, a step which could only be done on the grounds of a strong relation ship between the species concerned. I found no close resemblance between any o f the species of Blaeria and the new taxon.
The concept of a reduced ovary brought up the possible relationship with the genera having 2-celled ovaries with single ovules in each cell. These are Eremia, Grisebachia, Acrostemon, Simocheilus, Thoracosperma, Sympieza, Aniserica, Platycalyx and Coilostigma. After much examination of m aterial from these genera, I decided that there was no relationship of any significance between any representatives of these genera and the new taxon. There is a slight re semblance to the genus Eremia. This genus consists of seven species based mainly in the Ceres district (see No. 1 o f this series). The ovary in Eremia is either 4-, 2-or 1-celled, but always with a single ovule per cell and there are 8 stamens.
The relationship o f this taxon appears to me to to be with Erica and Blaeria and to some extent with Eremia, but it does not fit into any of them as presently constituted. From Erica it differs in having 4 stamens and a 2-celled ovary, from Blaeria in having 2 cells to the ovary and from Eremia in having 4 stamens and more than 1 ovule per cell. To change the generic limits o f any of these genera to force the inclusion of the new taxon would, in my opinion, be imprac ticable and would cause repercussions in the relation ships o f and differences between many other genera of the Ericoideae.
One hesitates to create genera, especially monotypic, in an already complex and highly variable subfamily, but after careful consideration I decided to describe this new taxon as a new monotypic genus and named it after its discoverer T. P. Stokoe. The combination of characters serving to characterise the new genus are the 2-celled ovary with usually 3 pendulous ovules per cell, rarely 2, 4, 5 or 6, and 3 bracteoles, a 4partite calyx, 4-lobed corolla and 4 free stamens.
The position of Stokoeanthus as outlined above is somewhat dubious. It would appear to belong to the Erica-Blaeria line of evolution with its reduc tion in ovary complement. On the one hand it ap proaches closely to Blaeria in the summation of charac ters, but not in its outward appearance. The only species of Blaeria occurring in the same general area are B. ericoides L., B. dumosa Wendl. and B. flexuosa Benth. On the other hand, its outward appearance is very Erica-like.
The variation in ovary arrangement needs further comment. A large num ber of flowers was examined mainly from spirit material of Oliver 4787, 4787a and 4790 to record ovary variation. The majority of ovaries contained 3 collateral, subapical, pendulous ovules in each cell. Occasional cells were found with 4 or 5 ovules and only a few with 2 or 6 ovules. In the ovaries where there were more than 3 ovules per cell, the ovules were arranged in two ranks, 3 above and 2 or 3 below, the lower rank being at the base of the swollen part of the placenta.
The calyx is described as 2-ranked. This needs further explanation. The adaxial and abaxial sepals are slightly broader than the two lateral sepals and overlap them to a small extent. This condition I have seen in other genera of the Ericoideae, but it is not comparable with the philippioid type occur ring in Philippia, Salaxis, Coccosperma, Scyphogyne, Lepterica, Nagelocarpus, Ericinella and Coilostigma. In these only the abaxial sepal is enlarged laterally as well as longitudinally, sometimes to a considerable degree.
Oliver 4787a is worth recording as it possesses double calyces. A part from this abnormality the flowers appear to be normal and functional. This col lection was probably a single shrub occurring amongst norm al flowered shrublets, but was not noted at the time of collecting.
In the area which I visited, the species grew in two separate populations on the south-facing slopes. The lower population (Oliver 4787) consisted of a small group o f scattered plants growing in a moist-type fynbos on a boulder-strewn slope and were undoubt edly outliers o f the much larger population 110 m higher up the peak.
The large population was confined to the southern end of the broad shale band of the Table M ountain Series. This is very prom inent at the summit of the Hottentots-Holland around Somerset Sneeukop. Here the species formed an alm ost pure community about 1 m high with an understorey o f low tussock grass.
Snow renders the shale band particularly con spicuous in winter. The large population is then frequently covered by snow sometimes even as late as mid-October when the shrubs are in flower. For this reason the specific epithet, chionophilus, was chosen.
The dull white to cream colour o f the flowers produces an unattractive shrub even though it flowers profusely. On being disturbed the shrubs gave off clouds of pollen. These two factors coupled with the enlarged stigma gave a strong indication o f wind pollination in the species.