Astrolobas are small, stem-forming, generally erect to leaning or even creeping, perennial, leaf succulents. Plants divide from the base to form small to large clusters, of which the central, oldest plants sometimes die off to yield a fairy ring-like arrangement. Stems can reach a length of about 0.5 m and, especially lower down, are covered in the remains of dead leaves, while the leaves in the upper part of a stem are green.

Fig. 2. Older astroloba specimens can sometimes develop a ‘fairy ring-like’ growth form, especially in cases where the nurse plant has died. Photo by S.M. Molteno.

New leaves emerge at the apical growth point of a stem, in a basic growth spiral (the generative spiral) that can be either clockwise or anticlockwise on each stem. As a result of the consistent angle between consecutive leaves on the stem of a plant (the divergence angle), the resulting leaf arrangement along a stem tends to form a pattern of (usually five) secondary leaf ranks or spirals. The divergence angles of different plants give rise to different spiral patterns (phyllotaxis).

Fig. 3. Astroloba leaves emerge around the central growth point in a regular spiral arrangement. This is known as the generative spiral, and it can be clockwise or anticlockwise at random. To show this, some of the leaves on these two stems (of the same Astroloba foliolosa specimen) have been numbered, according to their order of emergence. Photo by S.M. Molteno.

Fig. 4. These stems have generative spirals that go in the same direction (anticlockwise viewed from above). However, differences in the divergence angle, between two consecutive leaves, can lead to the five leaf ranks either spiralling in the same direction as the generative spiral (left); forming vertical ranks (centre); or spiralling in the opposite direction to the generative spiral (right). This is a very useful diagnostic character for astrolobas. Photos by S.M. Molteno.

The leaves are keeled, triangular, hard, and sharp-tipped. Leaf colour varies from various shades of green to bluish green to brownish, often with darker longitudinal stripes. Leaf texture is variable, ranging from smooth and shiny to rough and distinctly tuberculate, with a distinct, asymmetric keel. The leaf margins are usually smooth, but could also be finely toothed or tuberculate. In some species the margin loses its identity below the leaf tip.

Fig. 5. Variation in astroloba leaf ornamentation is demonstrated by the large, transversely arranged tubercles of the Astroloba bullulata specimen (left); the minute asperous tubercles of Astroloba corrugata (centre); and the longitudinal striations of the Astroloba pentagona specimen (right). Photos by S.M. Molteno.

Fig. 6. On some astrolobas, such as the Astroloba bullulata specimen on the right, one of the margins of each leaf lost its identity before the leaf tip. Photos by S.M. Molteno.

Inflorescences, which can reach a length of 0.6 m, carry the often widely spaced flowers in a raceme, which can rarely be branched. Pedicel (flower stalk) length is variable. In some species it is short, so making the inflorescences appear spike-like. The regular, tubular flowers are borne erectly or at least slanted upwards. In some species the perianth is longitudinally adorned with smooth or ruffled inflated tissue. The colour of the perianth (flower) lobes is variable. However, with one red-flowered exception (Astroloba rubriflora), the perianth tube is drab- to dull-coloured. Plants usually flower only once per year.

Fig. 7. The genus Astroloba has more floral diversity than any other alooid genus except for Aloe itself. The examples are, clockwise from the top left corner of the image: A. tenax, A. herrei, A. spiralis, A. rubriflora, A. spirella, and A. robusta. Photos by S.M. Molteno.

The morphological characters that define Astroloba are mostly its short, narrow stems; small, hard, sharp-tipped, more or less short-triangular leaves; the leaves that are variously arranged in five obvious or obscure ranks; as well as the more or less non-two-lipped flowers. When considered together, these characters warrant recognition of Astroloba as a genus separate from the other small aloes (a name indiscriminately applied to representatives of, inter alia, grass aloes, Aristaloe, Haworthia, and Haworthiopsis). Representatives of Astroloba were at first included in Haworthia, which itself was a segregate of the well-known genus Aloe. While Astroloba has morphological similarities with both Haworthia and Tulista, the suggested inclusion of Astroloba in Tulista does not adequately reflect genus diversity in the Alooideae, and that classification has not found favour. Along with Tulista, Haworthia, and Haworthiopsis, Astroloba is included in the cluster of genera referred to as ‘haworthioid’. With reference to these genera, ‘haworthioid’ recognises the comparatively small stature of the plants, as well as their generally dull-coloured flowers—there are notable exceptions, such as Astroloba rubriflora—borne on rather flimsy inflorescences.

The genus name is a combination of the Greek words aster and astros meaning ‘star’ and lobos meaning ‘lobe’. It refers to the star-shape formed by the spreading perianth (flower) lobes when viewed from above.

Based on both reproductive and vegetative morphological characters the most recent treatment of Astroloba regards the genus as consisting of two subgenera and four sections. These are: subgenus Astroloba in which four sections are recognised, and subgenus Poellnitzia.
Click on the links for a short description and images of the species:
Subgenus Astroloba section Astroloba includes A. bullulata, A. cremnophila, A. pentagona, A. tenax and A. tenax var. moltenoi. The species in this section have leaves that are often tuberculed, with one margin of each leaf usually losing its identity near the leaf apex. The relatively large divergence angle (±144°–151°) arranges the leaves in five ranks that appear either vertical or spiralling in the same direction as the generative spiral (although some Astroloba tenax specimens are exceptions). The inflorescence is often branched, and the flowers have dull grey or green perianth tubes with yellow lobes (although some Astroloba cremnophila specimens have cream lobes). The preferred habitat of all species in this section is relatively steep rocky slopes, in the far southwestern part of the Great Karoo. They occur from the Ceres-Tanqua Karoo in the west, to Prince Albert in the east.
Subgenus Astroloba section Intercedens includes A. corrugata and A. spirella. The species in this section have leaves that are matt. Their flowers have dull-coloured perianth tubes and cream-coloured lobes. The two species co-occur, and frequently hybridise with each other, in the western Little Karoo.
Subgenus Astroloba section Inflata includes A. herrei and A. spiralis. The species in this section have leaves that are matt and unadorned. The inflorescence is usually unbranched, and the flowers have somewhat inflated perianth tubes. The preferred habitat of both species is low, gentle slopes or flat plains usually comprised of rocky alluvium, on both the north and south sides of the Groot Swartberg mountain range.
Subgenus Astroloba section Vastora includes A. congesta, A. foliolosa and A. robusta. The species in this section have leaves that are glossy. Due to their relatively small divergence angle, the leaves form five ranks that are either vertical or spiral counter to the direction of the generative spiral. The flowers have relatively short pedicels and white lobes that often flare outwards. The three species are all relatively widespread, occurring on gentle slopes or level rocky terrain in the southern Great Karoo.
Subgenus Poellnitzia comprises a single species, A. rubriflora.