The genus is named for its stomach-shaped flowers ("gaster" is greek for "stomach") that result from the swollen base on the corolla. Common names include ox-tongue, cow-tongue, lawyer's tongue and, occasionally, mother-in-law's tongue.[2]
Gasterias are recognisable from their thick, hard, succulent "tongue-shaped" leaves. These are either in two opposite ranks (distichous), or in various distinctive spiral arrangements.[3] Their inflorescence is also unique, with their curved, stomach-shaped flowers, which hang from inclined racemes.
Distribution
Gasteria rawlinsonii 'Staircase' (a cultivar) showing the distinctive pendulous, "stomach-shaped" Gasteria flowers
The species of this genus are mostly native to the Eastern Cape Province, South Africa, where the bulk of the species occur – especially in the small area between Makhanda and Uniondale which enjoys rainfall throughout the year. However, the distribution of several species extends widely across the low-altitude coastal regions of the country, in an arched horseshoe shape across South Africa. At the one end of the genus's distribution, a species, Gasteria pillansii, extends into the far south-west corner of Namibia. At the other end, a species reaches the Lebombo mountains of Eswatini.
Taxonomy
Distribution map of the various Gasteria species and subspecies in southern Africa
Gasteria is part of the familyAsphodelaceae, subfamily Asphodeloideae. Closely related genera include Aloe and Haworthia, and the species of these genera are known to hybridise relatively easily with each other.[4]
Dividing Gasteria into species is extremely difficult, as each plant can be highly variable. One plant will look different depending on its location, its soil and its age. Young Gasteria plants typically look entirely different from older specimens. Usually, young plants have flat, strap-shaped, highly tubercled leaves, in a distichous formation.
In addition, the species tend to flow into each other in gradual transitions, with many intermediate forms, rather than being cleanly divided into discrete and separate species. Lastly, hybrids occur easily and naturally, whenever the range of two species overlap in habitat. There is therefore considerable disagreement on how many species exist, with as many as 100 names being listed.
Taxonomy according to flower morphology
Using morphology (especially flower structure), a traditional and widely accepted taxonomy was described in 1994 (van Jaarsveld et al.), dividing the genus into 2 sections, 4 series, and 16 species. E. J. van Jaarsveld has revised the taxonomy since then and the most recent synoptic review was published in 2007.[5] Several new species have been described in recent years, as well. Currently the number of accepted species is 29.
G. pillansii var. pillansii Kensit – western Cape Province
G. pillansii var. ernesti-ruschii (Dinter von Poellnitz) van Jaarsv. – south-west Namibia to north-west Cape Province (Richtersveld)
G. pillansii var. hallii van Jaarsv. – western Cape Province
Taxonomy according to genome
A phylogenetic study in 2005[13] suggest that the genus may be sub-divided into 5 groups with respect to an increasing pattern in DNA content and geographical distribution:
Gasteria bicolor eventually develops a short, sprawling stem. It has smooth, shiny, erect leaves
Gasteria baylissiana has distinctive tiny, white, truncate tubercles on both sides of its swollen, convex leaves, that have squarely truncated leaf-tips.
Gasteria ellaphieae forms rosettes of pointed, triangular, recurved, densely tuberculate leaves, and branched inflorescence.
Gasteria glomerata has distichous compact, round, glaucous, recurved rough-surfaced leaves, and forms dense clumps.
Gasteria vlokii forms rosettes of mat-surface, slightly rough, triangular (usually recurved), strap shaped leaves.
Adult Gasteria nitidas form rosettes of smooth, shiny, triangular leaves, with smooth (non-serrated) edges and true (non-marginiform) keels. Juvenile plants have recurved distichous, tubercled leaves.
Gasteria armstrongii is a very divergent form of Gasteria nitida which maintains into adulthood the dark, recurved, retuse, distichous, roughly tuberculate leaves.
Gasteria polita forms rosettes of short, triangular, smooth leaves, with rounded ends and strong keels
Gasteria doreeniae
Gasteria pulchra forms rosettes of smooth, thin, sharp, elongated, ascending leaves (linear triangular).
Large coastal group
Species generally form rosettes, with leaves usually bearing marginiform keels.
Gasteria carinata var carinata – the typical form. It has erect & spreading, rough, sparsely bumpy/tuberculate leaves
Gasteria batesiana has leaves which are heavily tuberculate (bumpy/warty) and finely rululous (wrinkled).
Cultivation
Gasteria species are grown in well-drained, sandy soils in light shade. The species can all be propagated by off-sets and cuttings (leaf cuttings can usually be rooted easily). They are also commonly propagated by seed. Germination usually occurs within 8 days but may take as long as one month depending on the species.
Flowering times vary between species, but is usually in the spring & summer.
Those in the summer rainfall areas to the east, tend to always flower in spring to summer (October–January in South Africa) such as Gasteria batesiana, Gasteria croucheri & Gasteria acinacifolia.
Those in the areas which receive rainfall all year, usually flower also in later summer (December–January) such as Gasteria excelsa, Gasteria nitida, Gasteria vlokii and Gasteria brachyphylla var. bayeri. Others in this region flower all year, but with a peak in the spring, such as Gasteria rawlinsonii, Gasteria bicolor & Gasteria carinata.
The westernmost species vary in their flowering times, within the species. Gasteria pillansii in the far west, flowers in summer (December–January), except for its northernmost variety "var. ernesti-ruschii" which flowers in autumn (March–April).
Gasteria disticha usually flowers in spring, but in the far north of its range near Beaufort West it flowers in December.[14]
Gasteria species are prone to Fusarium root rot, if they are over-watered.
[15][16]
Several hybrids with species in other related genera have been created in cultivation, such as between Gasteria and Aloe (× Gasteraloe), and between Gasteria and Haworthia (×Gasterhaworthia).
^Bailey, L.H.; Bailey, E.Z.; the staff of the Liberty Hyde Bailey Hortorium. (1976). Hortus third: A concise dictionary of plants cultivated in the United States and Canada. Macmillan, New York.
^Molteno, S. (2022). Phyllotaxis in Asphodelaceae subfam. Alooideae: a tool in taxon delimitation. Haseltonia, 28(1), https://doi.org/10.2985/026.028.0107
^van Jaarsveld, E. J. (2007). The genus Gasteria: a synoptic review (new taxa and combinations), Aloe, 44 (4), pp. 81-104.
^van Jaarsveld, E. J. (2014). Gasteria barbae, a new cliff-dwelling species from the Western Cape, South Africa, CactusWorld, 32 (4), pp. 257-260.
^Crouch, N.R., Smith, G.F. and Styles, D.G.A. (2011). Gasteria croucheri subsp. pondoensis, a new cremophyte from Pondoland, South Africa, Bothalia, 41, pp. 183-185.
^van Jaarsveld, E. J. (2014). Gasteria loedolffiae (Asphodelaceae). A new cliff-dwelling species from the Eastern Cape, South Africa, Bradleya, 32, pp. 44-49.
^van Jaarsveld, E. J. (2017). Gasteria koenii, a New Gasteria Species from the Swartberg, Western-Cape, South Africa. Haseltonia, 23, pp. 48-52.
^van Jaarsveld, E.J., Zonneveld, B.J.M., and Tribble, D.V. (2019). Gasteria langebergensis, a new status for a Gasteria from the Western Cape, South Africa. Bradleya, 37, pp. 167-171.
^van Jaarsveld, E. J. (2020). Gasteria visserii van Jaarsv., a new species from the Eastern Cape, South Africa. Bradleya, 38, pp. 26-29.
^van Jaarsveld, E. J. and Molteno, S. (2020). Gasteria camillae van Jaarsv. & Molteno, a new obligatory cliff-dwelling species from the Eastern Cape, South Africa. Bradleya, 38, pp. 20-25.
^B. J. M. Zonneveld, E. J. van Jaarsveld: Taxonomic implications of genome size for all species of the genus Gasteria Duval (Aloaceae). 24 Feb 2005
^E.J. van Jaarsveld: Gasterias of South Africa, A new revision of a major succulent group. Fernwood Press, Cape Town. p.19. ISBN1-874950-01-6
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