R.H. Archer

Bark Structure and Intergeneric Relationships of Some Southern African Cassinoideae (Celastraceae)

At present Cassine in southern Africa is treated in a wide sense (s.l.), including amongst others Allocassine p. p., Cassines. str., Crocoxylon, Elaeodendron, Lauridia, and Mystroxylon. A comparative anatomical study was made of mature bark representing 16 southern African species of Cassine s.l., and the monotypic Allocassine, Hartogiella and Maurocenia (all members of the subfamily Cassinoideae). Six bark types are distinguished on the basis of the type of sclerenchymatous elements in the secondary phloem; presence or absence of styloid crystals, e1astic threads, and sclerified phelloderm; stratified homogeneous phellem; and degree of rhytidome development. These correlate to a considerable extent with the generic subdivision of Cassine s.l. proposed by Loesener (1942) and Robson (1965). On the basis of bark anatomy and other evidence, it is proposed that the circumscription of Cassine be restricted to include only the southern African species C. peragua and C. parvifolia, and possibly Hartogiella. Crocoxylon, Elaeodendron, Lauridia and Mystroxylon should be reinstated or maintained, although with some modification of the originally defined generic limits.

Wood Structure and Generic Status of Some Southern African Cassinoideae (Celastraceae)

Opinions differ on whether to treat Cassine in southern Africa in a wide sense, or to recognise several segregate genera, such as Elaeodendron, Crocoxylon, Lauridia, Mystroxylon and Cassine s. str. A comparative anatomical study was made of mature wood representing 17 southern African species of Cassine s.l., Pleurostylia and the three monotypic genera, Allocassine, Hartogiella and Maurocenia (all members of the subfamily Cassinoideae). The wood structure is described with emphasis on the taxonomic value of quantitative and qualitative characters. Various features were found to be diagnostic at supraspecific level. The presence or absence of scalariform perforation plates, septate fibres, various ray types, and additional quantitative characters could be useful for taxonomic application, especially for generic delimitation. Three principal wood types, of which one encompasses three subtypes, are recognised among the species examined. Wood anatomical evidence tells against a wide generic concept for Cassine, and favours the recognition of segregate genera.

Palynology and intergeneric relationships in some southern African species of subfamily Cassinoideae (Celastraceae)

Abstract It has long been a matter of controversy whether to treat Cassine L. in southern Africa in a wide sense, or to recognize several segregate genera, such as Elaeodendron Jacq. f., Crocoxylon Eckl. & Zeyh., Lauridia Eckl. & Zeyh., Mystroxylon Eckl. & Zeyh. and Cassine s. str. The pollen morphology of the 14 southern African species currently included in Cassine s.l., as well as the three monotypic genera Allocassine N. Robson, Hartogiclla Codd, and Maurocenia Mill., has been studied by means of LM, SEM and TEM. Pollen grains in all species shed as monads, radially symmetrical, isopolar, tricolporate with colpus membranes conduplicate, tectate, subspheroidal, 14–30 μm in equatorial and 13–37 μm in polar diameter. On the basis of sexine sculpture three pollen types are recognized. Pollen type A (sexine reticulate) has been recorded in Maurocenia, Hartogiella, Cassine aethiopica, C. barbara, C. burkeana, C. eucleiformis, C. maritima, C. papillosa, C. parvifolia, and C. peragua; pollen type B (sexine fo...

Maytenus oleosa (Celastraceae), a new species from southern Natal and Pondoland

Maytenus oleosa Van Wyk & Archer, a small riverine tree endemic to the sandstone region of southern Natal/Pondoland is described. It is allied to M. undata (Thunb.) Blakelock from which it differs in a combination of characters, some of the more significant being the narrowly elliptic leaves which in dried specimens are green and glossy above, dull yellowish-green with the venation (including the reticulation) dark green or brownish and very conspicuous below; mesophyll and stomatal subsidiary cells of lamina with a profusion of relatively large oil droplets; black spots of an unknown substance nearly always appearing along veins of the lamina during preservation in FAA; pedicels articulated at or very near the base; sepals markedly unequal; petal margins ciliolate and the stigma subcapitate and not distinctly rugose or papillate. M. oleosa is a rare species, at present recorded only from watercourses between the Umtamvuna and Mzamba Rivers.

A taxonomic revision of Cassine L. s. str. (Cassinoideae: Celastraceae)

Cassine L, in southern Africa has been treated in a wide sense, as comprising several segregate genera, such as Eiaeodendron Jacq., Lauridia Eckl. & Zeyh., Mystroxylon Eckl. & Zeyh. and Cassine s. str. New evidence from palynology, macromorphology and anatomy supports the subdivision of Cassine s.l. into smaller, more homogeneous taxonomic units. Cassine in the strict sense, as revised here, includes three species, one with three subspecies, of shrubs or trees endemic to southern Africa. Most non-southern African species (approximately 30) previously referred to Cassine s.l. are best classified in Eiaeodendron. The monotypic genus, Hartogiella Codd, is not maintained but reduced to synonomy under Cassine.

Generic Delimitation of Subfamily Cassinoideae (Celastraceae) in Africa

It has long been a matter of debate whether to treat Cassine in a wide sense, or to recognize several segregate genera. The accumulation of new taxonomic evidence from palynology, macromorphology and anatomy, as well as other sources, leads to a better understanding of generic limits in the Celastraceae. Available evidence suggests that Cassine s.l. as currently circumscribed, is an extremely artificial taxon and best subdivided into smaller, more homogeneous units. Most of these groups correspond very closely with previously described segregate genera. Eight genera (Cassine s. str., Elaeodendron, Mystroxylon, Pleurostylia, Allocassine, Lauridia, Maurocenia and a still to be described new genus) are proposed for the African species of Cassinoideae. Cassine s. str. comprises three species endemic to southern Africa.

A taxonomic revision of Robsonodendron, a new genus in the Cassinoideae (Celastraceae)

Robsonodendron R.H. Archer, a new woody genus endemic to southern Africa, is described. Its two species have hitherto been included in either Cassine L. s. I. or Mystroxylon Eckl. & Zeyh. The affinities of the new genus are still obscure, although it shows some relationships with Mystroxylon and the Maytenus acuminata (L.f.) Loes. complex (subfamily Celastroideae), from which it differs in several important morphological, palynological and anatomical characters. A taxonomic revision of the genus is provided in which two new combinations, Robsonodendron eucleiforme (Eckl. & Zeyh.) R.H. Archer and R. maritimum (H. Bol.) R.H. Archer, are proposed.

A taxonomic revision of Lauridia Eckl. & Zeyh. (Cassinoideae: Celastraceae)

Evidence from macromorphology, anatomy and palynology, suggests the subdivision of the large and heterogeneous Cassine L. s.l., into smaller, more homogeneous genera. Lauridia Eckl. & Zeyh., as delimited here, includes two species of small trees or lianas endemic lo southern Africa. Hitherto the genus has either been considered as monotypic, based on Lauridia reticulata Eckl. & Zeyh., or it has been included in a widely circumscribed Cassine. Cassine tetragons (L.f.) Druce is transferred to Lauridia and the new combination L. tetragona (L.f.) R.H. Archer is proposed.

A new species of Maytenus (Celastraceae) from southern Natal and Transkei

Maytenus vanwykii R.H. Archer, a new species near-endemic to the sandstone region of southern Natal and Pondoland (Pondoland Centre), is described. In leaf and spine morphology it superficially resembles M. mossambicensis (Klotzsch) Blakelock, but it differs from that species in being dioecious and having a distinctive suffruticose habit, short peduncles, erect petals, and flowers with the stamens and style markedly exserted in male and female plants, respectively. M. vanwykii is a rare species, at present recorded only from coastal and coastal plateau grassland between Port Edward in the north and Mazeppa Bay in the south.

A taxonomic revision of Allocassine N. Robson (Celastraceae)

A taxonomic account is given of the genus Allocassine N. Robson (Cassinoideae, Celastraceae). Allocassine is an isolated monotypic genus remotely related to the other southern African Cassinoideae. A. laurifolia (Harv.) N. Robson is a liana occurring in the eastern parts of southern Africa, Zimbabwe and Mozambique.