Sunday, February 11, 2018

Bulbine bruynsii and its Relatives

Bulbine bruynsii, greenhouse-grown in Connecticut, January.

Bulbine is a genus of about 80 species in the family Xanthorrhoeaceae (which, as currently circumscribed, also includes aloes and Haworthia). Bulbines are a varied assemblage, including geophytic species, weedy annuals and a few small shrubs. The arid, winter-rainfall climatic zones of South Africa and Namibia are home to numerous tuberous species of Bulbine with succulent leaves; some of these are window plants or form haworthia-like rosettes, though surely the strangest and most horticulturally intriguing species is Bulbine bruynsii

Bulbine bruynsii in flower, mid-winter.
 Mature B. bruynsii plants consist of a small subterranean tuber, from which radiate thickened, yellowish roots that can sprout additional plantlets, so that a clonal colony is eventually established. The plants are totally dormant in the warmer months, with no above-ground growth. In the autumn, mature tubers send up a pair of leaves (sometimes three or four leaves in coddled cultivated plants), and then a raceme of bright yellow flowers in mid-winter. The leaves are highly succulent, more or less the size and shape of small cucumbers, supported by incongruously skinny stalks formed by the leaf bases. The foliage of B. bruynsii is marked by lumpy horizontal bands, which are red below and translucent on their upper surfaces. The translucent patches presumably allow sunlight to diffuse into the interior of the leaves for photosynthesis; B. bruynsii is sort of a multistory high rise window plant.

In its native habitat, B. bruynsii is confined to a small range on the edge of the coastal plain west of Bitterfontein, South Africa, where it grows in open areas among larger succulents and scrubby vegetation. In cultivation, it seems to be unfortunately finicky, requiring a cool winter growth period with very high light intensity, on the edge of what it is possible for me to provide in New England, even with a sunny greenhouse. Root rot is a problem, especially during the summer dormancy. A loose, completely mineral soil with lots of sharp sand, pumice and perlite seems to be beneficial.

Plants do form clumps from root-borne sprouts, but this takes years, so seed is probably the most practical method of propagation. The seeds are reluctant to sprout, though, much more so than with other bulbines that I have grown. Seeds sometimes germinate in old pots, a year or more after sowing, which suggests that the seed coat might need to be broken down. The next time I have some seed, I'll try lightly scarifying it by rubbing it around the palm of my hand with a little sand. One further complication: B. bruynsii is not self-fertile, so cross pollinating two different individuals is required for seed production.

Bulbine diphylla, material from east of Bitterfontein, Western Cape Province, RSA.
 Several other species of winter-growing Bulbine seem to be close relatives of B. bruynsii, with similar midwinter flowers and stalked gherkin leaves, though lacking the windowed bumps. Bulbine diphylla is a relatively common species around the Knersvlakte region of South Africa, from Vanrhynsdorp in the south, north to Bitterfontein. Where I have seen it, it doesn't occur in the characteristic Knersvlakte open quartz flats, but instead among more lush, scrubby vegetation on loamy soil outside of quartz patches. In the veld and under glass, B. diphylla seems to be a more vigorous plant that B. bruynsii, forming thick stands of plants from root sprouts.

Bulbine dactylopsoides, cultivated material via Lifestyle Seeds.
Bulbine dactylopsoides is another related species from the Knersvlakte area. Like its namesake, Dactylopsis, the hitchhiker plant (family Aizoaceae), it is a denizen of quartz flats. It is generally similar to B. diphylla, but with waxier, stubbier leaves; plants in habitat in particular have almost barrel-shaped foliage. Immature plants have single leaves that are rounded and lie very close to the soil, closely resembling the probably only distantly related B. mesembryanthemoides. Flowering sized specimens develop the paired leaves held up above the soil on a thin stalk that are characteristic of the B. diphylla group.

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