Astroloba

A. corrugata, Doornriviervlei farm

Astroloba genus (Uitewaal)

by Steven Molteno and Jakub Jilemicky

Astroloba species overview

• Astroloba bullulata L.Bolus (Uitewaal)
• Astroloba congesta (Salm-Dyck) Uitewaal
• Astroloba corrugata N.L.Mey. & Gideon F.Sm. 
• Astroloba cremnophila van Jaarsveld
• Astroloba foliolosa (Haw.) Uitewaal 
• Astroloba herrei (Uitewaal)
• Astroloba pentagona (Haw.) Uitewaal (previously listed as 'hallii')
• Astroloba robusta P.Reinecke ex Molteno, van Jaarsv. & Gideon F.Sm.
• Astroloba rubriflora (L.Bolus) Gideon F.Sm. & J.C.Manning 
• Astroloba spiralis (L.) Uitewaal
• Astroloba spirella (Haw.) Molteno&Gideon F. Sm. (previously listed as 'smutsiana')
• Astroloba tenax Molteno, van Jaarsv. & Gideon F.Sm.
• Astroloba tenax var. moltenoi van Jaarsv. & Gideon F.Sm.
• x Astrolista bicarinata (Haw.) Molteno & Figueiredo

Description

A genus of small and extremely beautiful succulent plants, from the southern Cape of South Africa.

In form they are caulescent, growing long column-like stems which are densely covered in succulent leaves. New stems branching from the base of the plant, and longer stems tend to keel over and ramble along the ground. The leaves are firm, hard, sharp-pointed, and have keels on the underside. The leaf arrangement can be with the leaves “stacked” in five vertical rows/tiers, or they can be twisted into a rosette (imbricate).  

A. robusta flower stem

Most of the species flower in summer, bearing slender inflorescences of small, tubular flowers, the lobes of which form a tiny star (the origin of the name of the genus – “astro-loba” = “star-lobe”). In habitat, the dead stubs of the inflorescences remain on the stems, long after they have dried out. By noting the leaves in between each dead inflorescence, one can see how much the stem has grown in that year, and a count of the dead inflorescence stems can give a rough estimate of the age of that particular stem. This confirms that Astrolobas are relatively slow growing.

The flowers of most species are adapted for insect pollination (and are therefore small and white). However the divergent species Astroloba rubriflora has the red flowers of a plant which is typically adapted to bird pollination (in this case, sunbirds).  

A. bullulata, Viskuil

Species and speciation

Two species, rubriflora and corrugata, are relatively well defined (although the latter has been known to hybridise with other astrolobas).The other species often do not have clear boundaries, and tend to gradually transition from one to another. While this could be from aeons of hybridisation, it is more likely simply before the speciation process is just not fully complete. The “species” have diverged and differentiated, but nothing has happened yet to finally divide them from each other. 

A. pentagona, Oskopvlakte

Roberts-Reinecke therefore recognises three large Astroloba “complexes”, which contain all the other Astroloba entities (other than rubriflora and corrugata). Within each complex, there is a gradation between the various constituent “species”: 

• The Bullulata complex; containing Astroloba bullulata, which becomes Astroloba cremnophila in the south, and which gradually becomes Astroloba pentagona and Astroloba tenax in the east. Eventually, in the extreme east, the tenax are sufficiently divergent to variety moltenoi. To the south, the pentagona become spirella, of the next complex…

• The Spiralis complex; containing Astroloba spirella (which connects this complex to the Bullulata complex to the north), Astroloba spiralis, and the disparate populations of Astroloba herrei.

• The Foliolosa complex; a group which all have a glossy sheen, containing Astroloba robusta in the west; Going eastwards it gradually becomes Astroloba foliolosa, and then Astroloba congesta in the far east. (Roberts-Reinecke decides to consider these all merely to be subspecies of one overarching “foliolosa” species, but other authorities disagree) 

A. spiralis, S of Oudtshoorn

The result is a beautiful and varied “terrain” of characteristics in this genus. There are peaks of extreme features in some spots; there are gentle slopes of gradual change between different forms; and there is an occasional cliff-face strictly dividing one species from another. Nature is anything but simple!   

A. herrei, Scholtzkloof

Astrolobas can hybridise in nature with other genera like Tulista or Haworthiopsis. In most cases it is A. corrugata with other plants. Well known is hybrid T. pumila (maxima) X A. corrugata, known as A. skinneri or bicarinata. This attractive hybrid was reported from several localities from Montagu to Barrydale. Other natural hybrids known to us are H. viscosa x A. corrugata or T. opalina x A. corrugata.  

A. foliolosa, Dunbrody

Habitat

Astrolobas are usually found growing within/under bushes, which provide some protection from the heat and the sun, and within which their seeds can safely germinate (“nursery bushes”). Older Astrolobas often lose their nursery bushes over time, and are therefore exposed to the bleaching, desiccating effect of direct sunlight. In habitat most Astrolobas show some damage from both the sun, and from grazing animals. Rock ledges and other landforms can also serve as protection within which Astrolobas can seed and thrive. 

typical locality of A. foliolosa at Steytlerville area

Distribution area

Astrolobas grow in Little Karoo and Great Karoo and their distribution area is from Roberston area (A. rubriflora) in the SW to Fish River in Eastern Cape (A. congesta). The most northern records sofar are Frasersburg and Middelburg (A. robusta). No plants have been reported from coastal areas.

The 'hotspot' for them seems to be Laingsburg area, where several species grow very close together. There are corrugata, spirella, bullulata, cremnophila, pentagona and robusta growing within several km and very often you can see intermediate forms.

Interesting plants are growing between Rooinek Pass and Prince Albert. These plants are tenax, tenax var. moltenoi and robusta.

A. robusta, near Willowmore

Cultivation

These plants are increasingly popular as succulent ornamentals, due to the extraordinary beauty of their leaf structure. Some have intricate patterns of lines, margins, spots and raised tubercles on their leaves. Nearly all of them display a crystal-like regularity in their leaf arrangement. This is not always apparent in wild plants, which are usually disfigured by their harsh habitat. 

In cultivation, they are at their best when provided with some protection from full sun. In a semi-shade environment, with extremely well-drained soil and gentle conditions, Astrolobas can become remarkably beautiful and ornate. 

Unfortunately, when conditions are not ideal, occasional random leaves can die, shrivel up and go brown, all along its stem. This is unfortunate because, as explained, much of the beauty of the plants comes from the intricate, crystalline pattern of their leaves. However this disfigurement can be avoided by keeping the plants in optimal, fertile conditions – growing steadily and sheltered from stress. 

A. spirella, near Joubertskop

All Astrolobas can be propagated by seed, by cuttings/offsets, and by division of clumps. Cuttings or offsets should be dried for several days to weeks, in a cool, shady environment, before being planted in well-drained sand. Seeds should be collected and sown on well-drained soil. It is optional to cover them with a very thin, fine layer of sand. Keep moist until they germinate, and continue to water regularly until they are relatively large and strong. Keep in a bright spot, but out of direct sunlight. 

Hybrids can be made between all the Astroloba species (except for rubriflora, which has evolved a highly distinct chemistry in its flowers). Astrolobas can also be hybridised with other related genera, such as Tulista, Haworthiopsis, Gasteria, Aristaloe, Gonialoe and Aloe themselves.  It is especially easy to hybridise with Gasteria and Tulista.

Astroloba cremnophila, N. Buffelspoort

A. congesta, near Committees Drift