Dicrocaulon humile

Dicrocaulon humile, J. Vlok collection from Rooiberg, north of  Vanrhynsdorp, W. Cape, S. Africa. Cultivated by Steven Hammer, Vista, Ca (early April 2011).

Dicrocaulon humile is a low-growing dwarf shrub, from the family Aizoaceae (ice plants), native to the arid Knersvlakte near the small town of Vanrhynsdorp in South Africa. Its highly succulent leaf pairs are fused into pea-like bodies, which are exposed and green only during the cooler months. This plant is very rarely cultivated, and as far as I know is represented in horticulture by a single clone derived from material collected at Rooiberg. There is a confusing abundance of hills and peaks in South Africa called "Rooiberg," but this one is the Red Mountain just northwest of Vanrhynsdorp. Dicrocaulon plants, like most mesembs, are self-infertile, so that the lonely D. humile of greenhouse collections does not set seed. However, cuttings taken early in the growing season in autumn root fairly easily, and the plant has been passed around among connoisseurs of such things to a limited extent.

Dicrocaulon humile in flower in cultivation in Connecticut, July 2015.

Dicrocaulon humile flowers right around the summer solstice, when the plants are otherwise dormant and brown. The flowers have subtle violet color, which doesn't show up very well in my photos, and a very strong sweet smell that I can detect from some distance. The odor is reminiscent of artificial grape soda. The blooms stay open day and night, but the fragrance is most pronounced during the heat of the day, suggesting pollination by bees or other daytime insects.

Dicrocaulon had long been considered part of a group of mesembs called the Mitrophyllum Group or Mitrophyllinae, consisting of about half a dozen minor genera with plants characterized by strict summer dormancy, heterophylly (producing different leaf shapes at different seasons, often with very distinct, compact summer resting leaves), and an epidermis with large, water-storing bladder cells. Recent evolutionary work (Klak et al. 2013. A phylogenetic hypothesis for the recently diversified Ruschieae) has split the former Mitrophyllum Group into two natural units that are only distantly related: the Dicrocaulon Clade comprising the genera Oophytum, Monilaria, Diplosoma and Dicrocaulon, which is basally diverging in the tribe Ruschieae, separate from a Mitrophyllum Clade consisting of Mitrophyllum and Meyerophytum, which originated more recently within the Ruschieae. The Dicrocaulon Clade plants have, in retrospect, exaggeratedly minute, shrivelled summer resting leaves that are quite different from the meaty oversummering bodies of the Mitrophyllum Clade genera.