Butterfly Crassulas

Succulent plants are somewhat rare in fynbos, especially compared to the Karoo to the north. But the stonecrop family, Crassulaceae, has a number of fynbos species. Most of these produce small flowers, pollinated by bees or even smaller insects. Two species though, Crassula fascicularis and Crassula coccinea, have large flowers that are adapted to be pollinated by moths and butterflies.

Crassula fascicularis (Crassulaceae)
Crassula fascicularis flowers start off white and fade to red
Crassula fascicularis (Crassulaceae)
Crassula fascicularis has long narrow succulent leaves and flowers clustered at the top

The commonest of these is Crassula fascicularis and it has flowers that show clear characters for moth-pollination. The flowers are held in a tight head at the end of a succulent stem with rather narrow leaves. “Fascicularis” refers to the way the flowers are held in a cluster or fascicle as it is sometimes referred to in botany. Each flower has a long tube that would only be accessible by the long proboscis of a moth or butterfly. The colour is usually white, although some yellowish green forms can be found through it range, with a dark red reverse. This helps the flower to “shine” at night, when visual stimuli are weakest. Finally, its greatest asset is the strong pervasive scent that it produces, but only during the hours of the night. The species is common in the western half of the Cape Floristic Region, from Swellendam to the Cape Peninsula and as far north as the Cederberg. Unlike many of the fynbos succulents, which are confined to rocky outcrops, this species can often be found growing in amongst the fynbos itself.

A very interesting study was conducted at Bains’ Kloof to confirm that moths were the intended pollinators of Crassula fascicularis. (Johnson et al. 1993. Moth pollination and rhythms of advertisement and reward in Crassula fascicularis (Crassulaceae). South African Journal of Botany 59: 511-513.) The study detected no pollinators during the day but at night geometrid moths were found with the pollen of Crassula fascicularis attached to their proboscides. The researchers also measured nectar and scent production across the hours of the day. While nectar production required a specialised technique, scent strength was measured using four blindfolded volunteers and determining how close the flower needed to be before they could detect the scent (I love the simplicity of this method and it could easily be replicated at home). The study found that around midday, there was almost no scent produced and very little nectar. Both increased rapidly during the afternoon to reach their highest level around midnight. After that they dropped again. So to appreciate Crassula fascicularis at its best, clearly a midnight walk on a still night is recommended.

Crassula fascicularis (Crassulaceae)
White flowers of Crassula fascicularis are scented at night to attract moths
Crassula coccinea (Crassulaceae)
Bright red flowers of Crassula coccinea attract the day-flying Mountain Pride Butterfly

Very closely related to Crassula fascicularis is Crassula coccinea. This species has not been found yet at Phillipskop but does grow on the neighbouring peaks of the Klein River Mountains. Crassula coccinea is a larger plant than Crassula fascicularis, with broader squatter leaves. It too has long-tubed flowers held in a cluster at the top of the stem, but the immediate striking difference is the colour of the flowers, which are a bright red. This colour is a strong visual stimulus for the Mountain Pride Butterfly, Aeropetes tulbaghia. It is eye-catching enough to attract the butterfly without further assistance and so Crassula coccinea does not produce any scent. Unlike Crassula fascicularis, Crassula coccinea is a plant more or less confined to rocky outcrops, where its flowers create easily spotted splashes of red against the rockface.

Despite their immediate differences, both species are closely related and belong to their own small section of Crassula, section Kalosanthes (there is a third species in the section not found near here, Crassula obtusa, which looks a bit like a squat few-flowered Crassula fascicularis). At one time they were even attributed their own genus, Rochea, but they are now considered part of the larger genus Crassula. Their genetic closeness is revealed in cultivation where they have been found to form hybrids with each other. In the wild, this is very unlikely to happen. Firstly, because they share different pollinators, but also because their flowering times are quite separate. Crassula fascicularis flowers in the spring, mainly September and October, while Crassula coccinea flowers in high summer peaking in January when the Mountain Pride Butterflies are on the wing.

Crassula fascicularis (Crassulaceae) flower
Crassula fascicularis flower has a long tube perfect for the proboscis of a moth

Like many succulents, both species are easy to grow from cuttings. They make good garden plants if given space, sunlight, and well-drained soil. Crassula fascicularis is rather short-lived, so needs regular replacing but as it roots so easily this is not hard to do and if the soil is right it often self-seeds. Crassula coccinea can be a bit more demanding of the right conditions but the large head of bright red flowers is worth the effort.

Crassula coccinea (Crassulaceae)
Crassula coccinea often grow on rocky ledges

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