Berger (1905) Berger (1908)

- Uitewaal (1940)

- Uitewaal (1947)

- Bertrand (1956)




Leptaloe Aloinella

Guillauminia Lemeea l


1 These seven genera are also recognized in the present chapter.

2 Apicra Willd. is a superfluous name for Haworthia Duval.

3 Apicra Haw. is a later homonym of Apicra Willd., applied to a group of haworthioid species, currently upheld as a separate genus. Although an attempt was made to conserve Apicra Haw. against Apicra Willd. (Stearn, 1939a, b), the genus was later renamed Astroloba by Uitewaal (1947).

4 Endlicher (1936) attributed Agriodendron to Haworth. However, this name could not be located in any of Haworth's publications. Jackson (1895) justifiably cites Endlicher as author of the name Agriodendron.

5 Chamaealoe, although published as a substitute name for Bowiea Haw., was superfluous at the time of publication. If Berger's (1905) generic concept is revived, a new name would therefore have to be given to what has been called Bowiea Haw. (nom. rej.) and Chamaealoe (nom. illeg.).

The opening up of distant lands, such as the southern African interior, by, amongst others Masson, Burchell and Bowie (Smith and Van Wyk, 1989), resulted in a steady stream of novel material reaching European botanical gardens. Botanists who had to deal with the wealth of new and undescribed specimens evidently did not know how to fit them into existing classifications and reverted to basing new genera on non-diagnostic, floral and/or vegetative structures or combinations of structures. However, in some circles the recognition of only a single genus, Aloe, for all the succulent-leaved, rosulate, alooid taxa persisted until at least the 1880s (Table 2.3). Clearly, a genus lies somewhere between these two extremes and, as Rowley (1976a) so aptly put it, '... the best we can hope to do is to avoid gross inconsistencies in our chosen unit,' — in this case the Aloaceae.

The taxonomic history of the Aloaceae started out conservatively in 1753. Of the genera currently classified in this subfamily, Linnaeus (1753) recognized only one, namely Aloe, which he included in his Class Hexandria Order Monogynia. Up to the time that Linnaeus proposed his sexual classification system, the few known alooid taxa, mainly comprised A. vera (L.) Burm.f., possibly of Arabia (Forster and Clifford, 1986), A. perryi Baker of Socotra (Lavranos, 1969; Horwood, 1971) and the South African A .maculata All. (Dandy, 1970), A. arborescens Miller, A. brevifolia Miller, A. commixta A.Berger, A. ferox Miller, A. glauca Miller, A. humilis (L.) Miller, A. plicatilis (L.) Miller, A. succotrina Lam. and A. variegata L. (Wijnands, 1983; Reynolds, 1950). These aloes were grouped mainly on the basis of their characteristic succulent leaves (Bauhin, 1651; Uitewaal, 1947; Rowley, 1960; 1976b). Although Linnaeus did not intentionally utilize vegetative characters in his classification system, the latter line of thought did, to some degree, precipitate in his treatment of Aloe. This is clearly illustrated by the inclusion in Aloe of taxa currently classified in Aloe, Astroloba, Gasteria, Haworthia (Reynolds, 1950; Bayer, 1976), Kniphofia (Codd, 1968) and Sansevieria Thunb. (Brenan, 1963; Wijnands, 1973). With the knowledge of hindsight, Linnaeus (1753) afforded Aloe and the New World Agave separate generic status, in contrast to other early taxonomists, such as Bradley (1716 1727) who, somewhat understandably, confused the two genera. Later researchers in the Aloaceae, for example Reynolds (1950, 1966) and Holland (1978) on Aloe sensu stricto, Van Jaarsveld (1994) on Gasteria and Bayer (1976, 1982, 1999) on Haworthia, have attempted natural classifications for these genera. Scott (1985), on the other hand, proposed an entirely artificial classification system for Haworthia, based mainly on vegetative characteristics.

Since the publication of the genus name Aloe (Linnaeus, 1753), this taxon has been plagued by taxonomic confusion. Linnaeus preferred a broad circumscription of this genus and his use of a limited number of reproductive characteristics as criteria for classification could not possibly provide conclusive evidence for generic circumscription in the Aloaceae. Furthermore, Linnaeus made extensive use of infraspecific categories for classification, one of his species, A. perfoliata, being burdened by 16 varieties. Although Reynolds (1950) established the identity of ten of these varieties, some remain obscure and cannot with certainty be linked to field populations.

Attempts to subdivide Aloe sensu Linnaeus (1753) started some 30 years after this heterogeneous entity was proposed (Table 2.3). Although this initial attempt (Medikus, 1786) to split Aloe into smaller, more homogeneous units was unsuccessful, the present-day circumscription of the four comparatively large genera, Aloe, Gasteria, Haworthia and Lomatophyllum dates from the early nineteenth century (Table 2.3). However, the Aloaceae does not consist of large genera only. Especially in the first half of the twentieth century genus names were proposed for several smaller units segregated from Aloe, Haworthia and Astroloba, the latter then being known as Apicra Haw. non Willd. (see footnote 3 of Table 2.3). This period coincided with the publication of the first plant classification systems based on phylogeny and probably represented attempts to display patterns of evolution within the alooid taxa. Of the genera proposed during this period, only Chortolirion and Poellnitzia are generally upheld, Astroloba having been recognized as a segregate of Aloe by the late nineteenth century (Baker, 1880).

Was this article helpful?

0 0
Aloe and Your Health

Aloe and Your Health

This іѕ а health guide, whісh саn hеlр people knоw hоw tо mаkе uѕе оf Aloe vera tо improve оvеrаll health аnd deal wіth mаnу kinds оf diseases.

Get My Free Ebook

Post a comment