Renamed in 2014 from Hypertelis acida (originally Pharnaceum acidum by Sir Joseph Dalton Hooker), Kewa acida is one of eight species in this recently-described genus. Through molecular phylogenetic research, it was also determined that Kewa represents its own family, so a new vascular plant family was erected: the Kewaceae.
It’s rare that we use a scan of a slide on Botany Photo of the Day, but for today something from a different technological era seems appropriate. It’s the twelfth anniversary since the first Botany Photo of the Day entry. Since the Garden’s director at the time, Dr. Quentin Cronk, was instrumental in establishing Botany Photo of the Day, I approached him to see if he had an image of Kewa acida, as I had recently read an article about it (link below). In an earlier part of his research career, Dr. Cronk published many papers on the plants of St. Helena, as well as a book, The Endemic Flora of St. Helena. It seemed like a reasonable request. An hour later, despite being in the field in Bermuda, Quentin replied with this scan of a slide, originally photographed in November, 1980!
As alluded to above, Kewa acida is endemic to the southern Atlantic Ocean island of Saint Helena. Its range is even more restrictive than that: south-facing slopes on the island, totaling an area not larger than 48km2 (18.5 sq. mi.) (more accurately it is 33km2–the following link explains the discrepancy). The small area of occurrence, the continued threat from introduced herbivores (first goats, then rabbits) and invasive plant species, and low population numbers have all contributed to an assessment that this is a IUCN CR or critically-endangered species. As plants range from annual to short-lived perennial life cycles, populations fluctuate from year to year depending on germination rates due to weather conditions. In 2012, 30129 mature plants were estimated; in 2013, only 3195.
One might think that a species on a remote oceanic island would have little impact on human history, yet Kewa acida was enough of a mainstay in the diet of oceanic travelers that it received the name “St. Helena salad plant”:
because its leaves were formerly often consumed as a vegetable high in vitamin C, necessary to fight off scurvy during or after long sea voyages. Its succulent leaves have a salty, acid [hence, acida] flavour and were used in salads in the past.
The quote above is from the article I previously mentioned as having read: Christenhusz et al. 2016. 852. Kewa acida (Kewaceae) Plant in Peril 39. Curtis’s Botanical Magazine. 33(4): 327-337. doi: 10.1111/curt.12167. If you are fortunate enough to have full access to the article, you’ll be able to check out the illustrations, descriptions, photographs, and cultivation information. If not, you can see Lucy Smith’s (palmsmithy@Twitter) beautiful illustration courtesy of Rebecca Hilgenhof’s tweet (PassifloraTree@twitter): Kewa acida.
Other than molecular aspects, what physical characteristics define the Kewaceae from where this genus was formerly ascribed (the Molluginaceae)? To quote from the Christenhusz et al. article again:
The eight species in this new genus and family were all well-known and circumscribed, but were previously associated with the genus Hypertelis E.Mey. ex Fenzl in Molluginaceae. Even though the flowers of species of Kewa Christenh. resemble those of Hypertelis, the vegetative morphology is strikingly different. Hypertelis has herbaceous stems and leaves in whorls, as is the case in many Molluginaceae, whereas Kewa has alternate, succulent leaves and usually woody stems, not unlike some Aizoaceae. Most remarkably, Kewa has a whorl of tepals of which the outer two are sepal-like, one is half sepal and half petal and the inner two are fully petal-like, an unusual flower morphology in Caryophyllales.
You can see the petal part of the above description in a photograph at the bottom of this page: APG – classification by consensus on the Kew Science blogs.