Cotyledon tanquana was named by the author in the American succulent journal Haseltonia in 2019, from plants collected in the Tanqua Karoo in 1993 (Van Jaarsveld 2019). Whilst on an expedition to Fraserburg and the Tanqua Karoo with my wife and 2 of our children on October 1993, we joined up with a friend Tielman Haumann, a local Lithops conservationist and expert who wanted to show us 2 species of Lithops endemic to the Tanqua region, as well as the small village Elandsvlei. On our way back Tielman arranged that we also briefly visited the farm Die Mond on the lower eastern foothills of the southern Cederberg in the Tanqua, to observe some San paintings and catch fish. Die Mond (the mouth) is a farm which consists of a shallow rocky gorge, and the confluence of several rivers draining the eastern slopes of the Skurweberg and southern Cederberg. These rivers, the Leeu-, Riet-, Brandkraals- and Matjiesrivier, then join the Doringrivier, the largest river system of the region (Taylor 1996). Along this gorge a Cotyledon was spotted and specimens gathered on 10 October, at the time thinking it was a form of the variable Cotyledon orbiculata.

 Fig. 7. Habitat of Cotyledon tanquana at Die Mond.

It was grown in the Botanical Society Conservatory at Kirstenbosch National Botanical Garden since its inception in 1997. Here the plant regularly flowered during winter to spring (August to October, southern hemisphere). The densely branched nature and sticky, cuneate, dull-green leaves and short corolla tube pointed to something unique and upon closer investigation, the plant was found to be distinct and named as a new species. In the winter of 2018, assisted by my wife Erma, Die Mond was re-visited and additional information gathered. 

Also, after another hiking expedition to the eastern Cederberg, arranged by Florent Gernier (French naturalist and intrepid explorer) on 18–21 November 2018, accompanied by the author and 2 students Nico van Wyk and Jaco Lategan, the species natural distribution was found to be wider than expected. This expedition on foot was from the farm Nuwerus (Rooi Sederberg), along the river to Die Mond, a route that goes through the heart of the eastern Cederberg. I was thus keen to join and hoping to find more plants. And indeed plants were found on cliffs adjacent to the river all the way to Die Mond farm. 

While I was working on the Cotyledon and Tylecodon book (Van Jaarsveld & Koutnik 2004), I was certainly aware of this taxon, but it was omitted because of the uncertainty of its status. Having revisited the habitat and taking into consideration its floral architecture, vegetative features and habitat, I decided to name it as a new species. The flowers for one, are reminiscent of C. tomentosa from the Klein Karoo and further east. The plants have some floral and vegetative features in common. The cliff-dwelling habitat (geology) of this taxon is also somewhat similar. The squamae are presented horizontally, transversely oblong, 2 × 1 mm, which is a unique feature. Squamae are nectar glands at the base of the floral tube. Most parts of the plant are covered in glandular hairs. C. tanquana has dull green leaves, which are distinctly cuneiform, with a glandular hairy surface, causing its stickiness.

The Tanqua Karoo is the closest desert to Cape Town. It lies in a rain shadow between the Cederberg and the escarpment mountains to the east. It has many unique species only confined to this region, which includes 2 species of Lithops (L. comptonii and L. werneri), Tanquana prismaticus, Didymaotus lapidiformis, Cephalophyllum alstonii and Mesembryanthemum clavatum.

The genus Cotyledon was established by Linnaeus in 1753, revised by Toelken in 1985 and also treated by the author in the Illustrated handbook of succulent plants (Crassulaceae) (Eggli 2003). Before 1978, all species of Tylecodon were part of Cotyledon. Toelken separated Tylecodon because of their spirally arranged leaves, becoming deciduous during the summer (Toelken 1978). Tylecodon is by far the largest genus (about 45 species) and is confined to the winter rainfall region.

Cotyledon is evergreen with leaves in opposite pairs. They vary from large shrubs 3 m tall, such as C. velutina, to flat-growing mat forming plants such as C. papillaris. Although Cotyledon grows widespread in drier parts of Africa, their greatest diversity is in the southeastern parts of South Africa The colourful, pendent, tubular flowers are large and conspicuous, and pollinated by sunbirds. The distribution of Cotyledon extends over southern and eastern Africa and as far as the Arabian Peninsula. Most Cotyledon species are endemic to South Africa. Toelken’s treatment (1985) was followed by Koutnik and the author’s book on Cotyledon and Tylecodon (2004), where eleven species have been treated (Van Jaarsveld 1997, 2003). Additional species since Toelken’s 1985 work that have been named, include C. eliseae (Van Jaarsveld 1997), C. pendens (Van Jaarsveld 2003), C. petiolaris (Van Jaarsveld 2015), C. gloeophylla (Van Jaarsveld 2015), C. xanthantha (Van Jaarsveld & Eggli 2017) and C. egglii (Van Jaarsveld 2017). Additionally, C. woodii was enlarged to accommodate the cliff-dwelling subsp. cremnophila (Van Jaarsveld 2015), as well as Cotyledon barbeyi var. soutpansbergensis (Van Jaarsveld 2017). Jacobsen (2017) has also proved that Cotyledon spuria L. (C. orbiculata var. spuria) should be raised again to species level (Toelken 1979). It grows sympatric with C. orbiculata var. orbiculata, differing not only in size and shape but also in their times of flowering. The genus Cotyledon has thus been enlarged and accommodates 17 species.