Systematic leaf anatomy of selected genera of southern African Alooideae (Asphodelaceae)

Abstract

Leaf anatomical features were studied in the taxonomically controversial Alooideae genera, Chortolirion Berger and Poellnitzia Uitewaal (both monotypic), as well as the aberrant Aloe bowiea Schult. & J.H. Schult. [= Chamaealoe africana (Haw.) Berger]. Particular reference is made to the taxonomic significance of epidermal characters in the subfamily. Previous claims that leaf cuticular sculpturing is under strong genetic control, and thus rather invariant, are contradicted by some infraspecific variation in patterning observed in at least Chortolirion and Aloe bowiea. Anatomical characters diagnostic for a particular genus were nevertheless evident in all samples of a species. Furthermore, scanning electron microscopic studies of both leaf surfaces proved to be invaluable in assessing variation patterns. Of particular taxonomic significance are the distribution and structure of the vascular bundles (presence/absence of enlarged parenchymatous cells in the inner bundle sheath), presence of palisade cells and location of crystalliferous idioblasts. Leaf anatomical data support the maintenance of Chortolirion and Poellnitzia as distinct genera, whereas Aloe bowiea falls within the range of variation previously reported for the genus Aloe. Blaaranatomiese kenmerke is ondersoek in die twee taksoriomies kontroversiële Alooideae-genusse, Chortolirion Berger en Poellnitzia Uitewaal, sowel as die afwykende Aloe bowiea Schult. & J.H. Schult. [= Chamaealoe africana (Haw.) Berger] Aandag word veral geskenk aan die taksonomiese nut van epidermale kenmerke in die subfamilie. Vorige beweringe dat blaarkutikulaskulptuur geneties streng beheer word, en dus min varieer, is teenstrydig met ’n mate van intraspesifieke variasie wat wel in die geval van ten minste Chortolirion en Aloe bowiea waargeneem is. Anatomiese kenmerke wat diagnosties is vir 'n bepaalde genus, is nietemin in alle eksemplare van 'n spesie waargeneem. Verder is skandeerelektronmikroskopiese ondersoeke van beide blaaroppervlaktes wenslik om sodoende die variasie in patrone teenwoordig by 'n spesie, vas te stel. Veral die verspreiding en bou van die vaatbondels (teenwoordigheid/afwesigheid van vergrote parenkiemagtige selle in die binneste bondelskede), teenwoordigheid van palissadeselle, en die ligging van kristalhoudende idioblaste is van besondere taksonomiese belang. Blaaranatomiese data verleen steun aan die behoud van Chortolirion en Poellnitzia as afsonderlike genusse, terwyl die blaaranatomie van Aloe bowiea binne die bestek van variasie val wat voorheen vir die genus vermeld is.