Within the section Otidia, Pelargonium alternans Wendl. is an easily recognisable taxon. It forms small, repeatedly branched, cushion-like shrubs with leaves growing alternately, which often results in branches that are zig-zag-shaped. The stems are succulent, becoming woody with age. The inflorescences are borne terminally on branches, are short and bear few-flowered inflorescences. The leaves and the petioles are visibly hairy, which sets this species apart from P. dasyphyllum, which also has persistent peduncles, although these are often difficult to observe in collections. Another interesting character of P. alternans is that the staminodes curve downwards during the phase when the pistil becomes ripe and anthers fall off. The most recent article by M. Becker and F. Albers introduced three subspecies: ssp. parviinflorescencs with few-flowered inflorescences and posterior petals sharply curved at the tips, ssp. longicalcar with hypanthia usually much longer than 10 mm, in addition to ssp. alternans [1].
In no description, Becker’s or older, are tubers mentioned. In fact, the easiest way to separate P. alternans from P. dasyphyllum used to be that the former should not have tubers.
However, this does not appear to be the case. In fact, two populations of what appeared to be P. alternans ssp. alternans have so far been observed to have tubers: one in the Anysberg Nature Reserve and just last year, another one in the eastern Cederbergs south of the Matjiesrivier Nature Reserve. The two locations are separated by about 150 km with the vast dry expanse of Tanqua Karoo between them.
It is unclear what this might mean in relation to taxonomy, however. The presence of tubers is not uncommon in the section of course, with tubers ranging from small round ones as is the case here (Fig. 1), to large thick rhizomes. The presence or absence of tubers is often taken as a character separating subspecies in the section, e.g. P. carnosum ssp. carnosum from P. carnosum ssp. ferulaceum or P. parviflorum ssp. parviflorum from P. parviflorum ssp. tuberculum. However, these subspecies seem to be geographically separated, whereas it is currently unclear if P. alternans populations with tubers are limited to the Klein Karoo and “adjacent” areas and even if so, if they overlap with populations without tubers.
My observations of cultivated plants with clear provenance have not revealed any further clones with tubers.
Fig. 1: Seedlings of P. alternans south of the Matjiesrivier Nature Reserve. These were re-planted after the photograph was taken.
Fig. 2: An adult flowering plant.
With the gradually reflexed petals (Fig. 2), the observed population seems to be the closest to P. alternans ssp. alternans. It is truly interesting how even taxa that have long been in cultivation and extensively studied, regularly surprise us.
By Matija Strlič, Ljubljana, Slovenia
Reference
- M. Becker, F. Albers (2010), Pollinator shift and speciation in P. alternans (Geraniaceae). Schumannia 6, 207-226.
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ISSN 2464-014X.
This article was first published in Geraniaceae Group News #169. Cite as: M. Strlič: Observations of tuberous P. alternans. Geraniaceae Group News #169 (2023), pp 28-31.