Uniquely Common

A curious aspect of living amongst the Cape Flora is that we sometimes forget how special some of our commoner plants actually are. A case in point is Saltera sarcocolla.  This species is found widely across the whole of the Klein River Mountains. It is found both at low and high altitudes, and while it has a preference for well-drained dry rocky slopes, it is not a particular habitat specialist. Furthermore, as it flowers on and off through most of the year, there is rarely a time that flowers cannot be found and it becomes so familiar that one forgets to notice it. This is a shame, not just because it is a beautiful plant, but because it is also, on a world scale, extremely localised. The entire range of the species is from the Cape Peninsula to Cape Agulhas, an area of less than 5,000 square kilometres – that is just 5% of the area of the Cape Floral Kingdom or 1/30,000 of the total land surface of the world.

Saltera sarcocolla (Penaeaceae)
Saltera sarcocolla has clearly protruding stamens

However, it is not just its restricted range that makes Saltera sarcocolla so unique, but that it belongs to a famly of plants that itself is restricted to the Cape Floristic Region, the Penaeaceae. Moreover, the species Saltera sarcocolla is quite isolated within that family and has therefore been placed in its own genus, the monotypic Saltera (monotypic means that a taxon has just a single subordinate taxon within it). The Penaeaceae are a family of about 23 species. Its closest relatives are the trees belonging to the small African families of Oliniaceae (containing just Olinia with 8 species) and Rhynchocalycaceae (also monotypic, with just a single species), and which are sometimes included within it. The true Penaeaceae though are all shrubs, easily recognised by their opposite squarely pointed leaves that are held in four overlapping rows up the stem. This has given them the common name of the Brickleaf Family. The flowers too have their parts in fours, whether it be four flowers in the inflorescence, four petals, four stamens, four lobes to the stigma, or four compartments in the ovary.

Saltera sarcocolla (Penaeaceae) habit
The habit of Saltera sarcocolla is of a loose clump of sparsely erect stems
Saltera sarcocolla (Penaeaceae) leaves
Overlapping acutely pointed leaves of Saltera sarcocolla make the stem look square

Within the family, the genus Saltera is most similar to another small genus of just two species, Sonderothamnus. The two species of Sonderothamnus are even more restricted in their range. Sonderothamnus petraeus is only found on rocky outcrops in the Kogelberg, while Sonderothamnus speciosus is restricted to the area in and around the Klein River Mountains. The two genera differ in the number of ovules in each compartment of the ovary. So while Sonderothamnus has two ovules per locule, Saltera has four. This is obviously not an easy character to observe but fortunately in the field there are more evident features. Saltera sarcocolla has the stamens protruding far beyond the petals, whereas in Sonderothamnus, the stamens are held right at the mouth of the flower tube. The plants of Saltera sarcocolla have many loose stems and form quite broad, if untidy shrubs, about as wide as high, with greyish-white or silvery mealy leaves. The plants of Sonderothamnus speciosus often have just a single stem and the leaves are a normal plain green. While Saltera sarcocolla is very common Sonderothamnus speciosus is rare, very localised in its distribution, and where it does occur it is usually only found as a couple of plants scattered in the fynbos.

Sonderothamnus speciosus (Penaeaceae)
The stamens of Sonderothamnus speciosus do not protrude beyond the mouth of the flower
Sonderothamnus speciosus (Penaeaceae)
The plants of Sonderothamnus speciosus have only one or two branches
Saltera sarcocolla (Penaeaceae) habitat
Saltera sarcocolla rarely forms an impressive display, as the flowers appear on and off over a long period

The genus name is given in honour of Paymaster-Captain Terence Salter, who was based at Simonstown Naval Base, before eventually emigrating permanently to South Africa. He was best known for his work on Oxalis and for producing the first Flora of the Cape Peninsula in conjunction with Robert Adamson. Captain Salter also published a small note in 1940 on the genus Sarcocolla, as it was then known, where he was the first to consider that it comprised of a single variable species. In 1958, it was determined that the genus name Sarcocolla had already been used for another plant and therefore Bullock renamed the genus after Captain Salter himself.

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