All you wanted to know about Haworthias, Gasterias and Astrolobas: Astroloba tenax

Astroloba tenax, W. Vrischgewaagd

Astroloba tenax Molteno, van Jaarsv. & Gideon F.Sm.
by Jakub Jilemicky and Steven Molteno

tenax: ("tenacious") referring to the habitat, usually on exposed north-facing slopes or cliffs

This newly described species is indigenous to the Prince Albert Succulent Karoo, with a range that is mostly west of Prince Albert. It grows on steep, exposed, rocky slopes, often close to A.herrei (which grows on the lower slopes), and A. robusta (which grows on the gravelly flats). None of these three species hybridise though, as their flower shape and flowering times are different.

Distribution map

Astroloba tenax is very variable in its leaf form and size. Its leaves are usually shiny, somewhat recurved, with darker margins and keels that often have white spots or tubercles. One of the margins of each leaf sometimes fades near the leaf tip - a character normally seen in its closest relatives: A. pentagona, A.cremnophila and A.bullulata. Astroloba tenax seems to be connected through intermediate pentagona populations near Gamkapoort Dam to the main pentagona populations further West.

Astroloba tenax, W. Vrischgewaagd

The key diagnostic character of Astroloba tenax is its flowers, which are small, grey, tubular, and a bit closed at the apex. The lobe tips are yellow and they do not open up much. The flowers are on a tall, thin inflorescence that is often branched. The flowers appear in summer.

North east of Prince Albert are outlying populations of A. tenax that are unusually large - the largest in the whole genus. Plants here attain enormous sizes, with shiny leaf surfaces and varied combinations of tubercles and striations. Gideon Smith and Ernst van Jaarsveld published this variety as A.tenax var moltenoi. This variety was sometimes confused with the East Asian horticultural cultivar "Silver-horn" ("gintsuno"), but Silver-horn's flowers reveal it most likely to be an x Astrolista hybrid.