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Plant Highlight: Gasteria armstrongii
by Brian Kemble
About the Genus
The genus Gasteria is related to the larger genus Aloe, and these are placed in the family Asphodelaceae. The leaves of the various species are generally tongue-like or sword-like, with or without spots, and with textures varying from smooth and glossy to rough and granular. When Ernst van Jaarsveld published his monograph on the genus Gasteria in 1994, he recognized 16 species. That number has risen in the years since, and the Monocots volume of the Illustrated Handbook of Succulent Plants (revised edition, published in 2020) lists 26 species.
Area of Occurrence
All of the Gasteria species are from southern Africa, and they are found in a band extending from the winter-rainfall region along South Africa’s west coast to the eastern summer-rainfall part of the country. Many of them occur near the southern coast, where there is some rainfall in both winter and summer, and this is true for Gasteria armstrongii, though it gets more rainfall during the summer months than in winter. It has a very small area of occurrence in the coastal flats near Jeffreys Bay, Eastern Cape Province.
About the Plant
It is very common for Gasteria seedlings to have their leaves in a distichous arrangement (the leaves all in one plane, stacked atop one another on either side of the central growing point). In some species, this changes as the plant matures, giving way to mature plants with leaves extending in all directions. In other species, mature plants remain distichous, as is the case with G. armstrongii. Its close relative G. nitida looks very similar as a seedling, but at maturity it develops into a rosulate plant with triangular leaves. For a time, G. armstrongii was considered to be a variety of G. nitida (like a perpetuated juvenile form), but it is now considered a separate species. The leaves of G. armstrongii are dark green, thick, stubby and tongue-like, sometimes tapering to a pointed tip, but often blunted or truncated (although with a tiny sharp tip, or mucro). The leaves usually have a bumpy surface, but the bumps are smoothed, as if the leaf had been sanded. Occasionally, plants can be found without bumps and with scattered white spots, but this is unusual. Plants grown in bright light can get a very dark blackish green, or under very dry conditions they can become flushed with reddish-brown. While some plants remain single-headed, others produce a few offsets to make a small clump. On a mature plant, the leaf length varies from 1.2 to 2.4 inches (3 to 6 cm), with a width of up to 1.4 inches (3.5 cm). In nature, plants are sometimes shaded by small shrubs or other adjacent vegetation, and this results in the leaves being entirely above-ground. When fully exposed, the plants can pull down into the soil. leaving only the upper leaf surfaces exposed. If soil or leaf litter accumulates on top of them, they can be quite cryptic and difficult to spot.
Pictures taken in habitat
About the Flowers and Fruits
G. armstrongii is a summer-flowering species, with its peak flowering period coming in January and February in its South African home, or in July and August at the Ruth Bancroft Garden. The inflorescence does not branch, and it is up to 20 inches long (50 cm), usually ascending erectly, though it may incline a little. The number of flowers per inflorescence is variable, but a robust one may hold over 40 flowers, which dangle against the stalk. Each flower has a slender curved pedicel about .2 inch to .24 inch long (5 to 6 mm), while the flower itself is from .79 inch to .95 inch long (20 to 24 mm). The flower is curved and tubular, with the basal part somewhat enlarged (though not as dramatically as with some other species in the genus). This basal portion is coral reddish-pink or red-orange in color, and it comprises half the flower or a little more. The remainder of the flower is paler and narrower, with a slight flaring at the mouth. The tube of the flower separates into 6 tepals toward the mouth, 3 outer and 3 inner (this is true of all Gasteria species, as well as their relatives the aloes). Crowded within the mouth of the flower are the 6 stamens and the central pistil, the latter arising from the swollen ovary at its base. The stamens hold the pollen-bearing anthers, and being grouped at the flower’s mouth puts them where they can dust a visiting sunbird when it comes to drink the nectar held within the tube. Though they are pollinated by sunbirds in nature, the flowers of G. armstrongii are equally appealing to hummingbirds, which regularly visit them at the Ruth Bancroft Garden. A pollinated flower develops an oblong capsule, green at first, but then turning a pale grayish-brown at maturity and splitting open to release the seeds. The flattened, flake-like black seeds are stacked in 3 chambers within the capsule, and they are about .12 inch to .16 inch long (3 to 4 mm).
Plants in Cultivation
This species is not difficult to grow, and although it is most often seen as a potted plant, it can also be grown in the garden in places where the temperatures don’t drop much below freezing in winter. Note, however, that it is slow-growing. In hot interior climate zones, it shoud be given some shade, but it cool coastal climates it can take full sun, though it will grow happily in shadier positions as well. As with most Gasteria species, a severed leaf can be rooted, and eventually it will produce new plants at its base. When these have become large enough, they can be removed and grown on.
