Abstract
BackgroundAloe vera supports a substantial global trade yet its wild origins, and explanations for its popularity over 500 related Aloe species in one of the world’s largest succulent groups, have remained uncertain. We developed an explicit phylogenetic framework to explore links between the rich traditions of medicinal use and leaf succulence in aloes.ResultsThe phylogenetic hypothesis clarifies the origins of Aloe vera to the Arabian Peninsula at the northernmost limits of the range for aloes. The genus Aloe originated in southern Africa ~16 million years ago and underwent two major radiations driven by different speciation processes, giving rise to the extraordinary diversity known today. Large, succulent leaves typical of medicinal aloes arose during the most recent diversification ~10 million years ago and are strongly correlated to the phylogeny and to the likelihood of a species being used for medicine. A significant, albeit weak, phylogenetic signal is evident in the medicinal uses of aloes, suggesting that the properties for which they are valued do not occur randomly across the branches of the phylogenetic tree.ConclusionsPhylogenetic investigation of plant use and leaf succulence among aloes has yielded new explanations for the extraordinary market dominance of Aloe vera. The industry preference for Aloe vera appears to be due to its proximity to important historic trade routes, and early introduction to trade and cultivation. Well-developed succulent leaf mesophyll tissue, an adaptive feature that likely contributed to the ecological success of the genus Aloe, is the main predictor for medicinal use among Aloe species, whereas evolutionary loss of succulence tends to be associated with losses of medicinal use. Phylogenetic analyses of plant use offer potential to understand patterns in the value of global plant diversity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0291-7) contains supplementary material, which is available to authorized users.
Highlights
Aloe vera supports a substantial global trade yet its wild origins, and explanations for its popularity over 500 related Aloe species in one of the world’s largest succulent groups, have remained uncertain
Succulent plants are usually associated with arid environments; numerous aloes occur in the drylands of Africa, they are abundantly represented in tropical and subtropical vegetation infrequently impacted by drought
Low levels of genetic polymorphisms, taxonomic complexities, and the number of inaccessible, narrowly distributed species challenge the study of aloes; this is the first phylogeny to include >10% of Aloe species
Summary
Aloe vera supports a substantial global trade yet its wild origins, and explanations for its popularity over 500 related Aloe species in one of the world’s largest succulent groups, have remained uncertain. Aloe (>500 species) is by far the most speciose of the six genera known collectively as aloes, which include Aloiampelos (7 species), Aloidendron (6 species), Aristaloe (1 species), Gonialoe (3 species) and Kumara (2 species) They are iconic in the African flora, and occur predominantly in eastern sub-Saharan Africa, and on the Arabian Peninsula, Madagascar and western Indian Ocean islands. Most are habitat specialists with narrow ranges and extraordinary rates of endemism, from an estimated 70% in southern Africa, 90% in Ethiopia, to 100% on Madagascar [8] These centres of diversity coincide alarmingly with Africa’s biodiversity Hotspots, where a highly endemic biota is under substantial threat of extinction [9]. It has not been possible to determine whether Aloe vera is phylogenetically distinct from its many relatives, nor whether such phylogenetic distance may account for any potentially unique properties underpinning the value of the succulent leaf tissue
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