Abstract
The confident identification to species rank of fragmentary and sterile plant material is often challenged by the absence of diagnostic characters, which are present in intact specimens, reproductive parts, and plants in habitat. Here, we consider leaf surface micromorphology for the identification of the genus Aloe in the Horn of Africa region. Primary and secondary sculpturing of the leaf epidermis and stomata were characterised from SEM micrographs of 35 taxa representing 31 species of Aloe (Asphodelaceae subfam. Alooideae). Detailed comparison revealed that leaf surface characters are conserved between species and within-species variation is modest. Closely related taxa in the Aloe adigratana—A. camperi—A. sinana species complex could be distinguished using leaf surface micromorphology alone. These characters also guide species delimitation; in the species complex including A. schoelleri and A. steudneri, a narrow circumscription is supported, whereas with
A. ankoberensis and A. pulcherrima, a wider circumscription merits consideration. The observed trait combinations are characteristic of plants in xeric environments, with the most notable feature being stomata that are most deeply sunken in species in more arid habitats. Our findings support the use of comparative study of micromorphological leaf surface characters for species identification and taxonomy in the genus Aloe.
References
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Cutler, D.F., Botha, T. & Stevenson, D.W. (2007) The epidermis. In: Cutler, D.F., Botha, T. & Stevenson, D.W. (eds.) Plant anatomy: an applied approach. Blackwell Publishing Ltd, Oxford, pp. 76–93.
Cutler, D.F. & Brandham, P.E. (1977) Experimental evidence for the genetic control of leaf surface characters in hybrid Aloineae (Liliaceae). Kew Bulletin 32: 23–32. https://doi.org/10.2307/4117256
Cutler, D.F., Brandham, P.E., Carter, S. & Harris, S.J. (1980) Morphological, anatomical, cytological and biochemical aspects of evolution in East African shrubby species of Aloë L. (Liliaceae). Botanical Journal of the Linnean Society 80: 293–317. https://doi.org/10.1111/j.1095-8339.1980.tb01666.x
Engler, A. (1895) Die Pflanzenwelt Ost-Afrikas und der Nachbargebiete, Vol. 2. D. Reimer, Berlin, 433 pp. https://doi.org/10.5962/bhl.title.587
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Fradera-Soler, M., Rudall, P.J., Prychid, C.J. & Grace, O.M. (2021) Evolutionary success in arid habitats: morpho-anatomy of succulent leaves of Crassula species from southern Africa. Journal of Arid Environments 185: 104319.
Gilbert, M.G. & Demissew, S. (1992) Notes on the genus Aloe in Ethiopia: misinterpreted taxa. Kew Bulletin 47: 647–653.
Gilbert, M.G. & Sebsebe Demissew. (1997) Further notes on the genus Aloe in Ethiopia and Eritrea. Kew Bulletin 52: 139–152. https://doi.org/10.2307/4117846
Glen, H.F. & Hardy, D.S. (1995) Aloe section Anguialoe and the problem of Aloe spicata L.f. (Aloaceae). Haseltonia 3: 92–103.
Grace, O.M. (2011) Current perspectives on the economic botany of the genus Aloe L. (Xanthorrhoeaceae). South African Journal of Botany 77: 980–987. https://doi.org/10.1016/j.sajb.2011.07.002
Grace, O.M., Buerki, S., Symonds, M., Forest, F., van Wyk, A.E., Smith, G.F., Klopper, R.R., Bjorå, C.S., Neale, S., Sebsebe Demissew, Simmonds, M. & Rønsted, N. (2015) Evolutionary history and leaf succulence as explanations for medicinal use in aloes and the global popularity of Aloe vera. BMC Evolutionary Biology 15: a29. https://doi.org/10.1186/s12862-015-0291-7
Grace, O.M., Klopper, R.R., Figueiredo, E. & Smith, G.F. (2011) The aloe names book. Strelitzia 28. South African National Biodiversity Institute and the Royal Botanic Gardens, Pretoria and Kew, pp. 1–3.
Grace, O.M., Klopper, R.R., Smith, G.F., Crouch, N.R., Figueiredo, E., Rønsted, N. & van Wyk, A.E. (2013) A revised generic classification for Aloe (Xanthorrhoeaceae subfam. Asphodeloideae). Phytotaxa 76: 7–14. https://doi.org/10.11646/phytotaxa.76.1.2
Grace, O.M., Simmonds, M.S.J., Smith, G.F. & Van Wyk, A.E. (2009) Taxonomic significance of leaf surface morphology in Aloe section Pictae (Xanthorrhoeaceae). Botanical Journal of the Linnean Society 160: 418–428. https://doi.org/10.1111/j.1095-8339.2009.00982.x
Ickert-Bond, S.M., Harris, A.J., Lutz, S. & Wen, J. (2018) A detailed study of leaf micromorphology and anatomy of New World Vitis L. subgenus Vitis within a phylogenetic and ecological framework reveals evolutionary convergence. Journal of Systematics and Evolution 56: 309–330. https://doi.org/10.1111/jse.12313
Jayeola, A.A. & Thorpe, J.R. (2000) A scanning electron microscope study of the genus Calyptrochilum Kraenzl. (Orchidaceae) in West Africa. Feddes Repertorium 111 (5–6): 315–320. https://doi.org/10.1002/fedr.20001110506
Klimko, M. & Wiland-Szymanska, J. (2008) Scanning electron microscopic studies of leaf surface of taxa of genus Dracaena L. (Dracaenaceae). Botanika—Steciana 12: 117–127. https://doi.org/10.1021/1a9017322
Koch, K., Bohn, H.F. & Barthlott, W. (2009) Hierarchically sculptured plant surfaces and superhydrophobicity. Langmuir 25: 14116–14120. https://doi.org/10.1021/la9017322
Li, X., Yang, Y., Henry, R.J., Rossetto, M., Wang, Y. & Chen, S. (2015) Plant DNA barcoding: from gene to genome. Biological Reviews of the Cambridge Philosophical Society 90: 157–166. https://doi.org/10.1111/brv.12104
Linnaeus, C. (1753) Species Plantarum, Vol. 1. Impensis Laurentii Salvii, Stockholm, 560 pp. https://doi.org/10.5962/bhl.title.37656
Lubbinge, J. (1971) ’n Studie van die anatomiese bou van twee stingels en vier bloei-asse van die genus Aloe. Aloe 4: 13–28.
Medhanie, G. & Dioli, M. (2006) Observations on three poorly known aloes from Eritrea. Cactus & Succulent Journal 78: 36–41. https://doi.org/10.2985/0007-9367(2006)78[36:ootpka]2.0.co;2
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