Another entry from Taisha, who writes:
Today, we have several photographs of Pereskiopsis aquosa from retired Garden staff member, David Tarrant. Thanks for sharing, David! David mentioned in his email to us that this is currently flowering in his garden after the commencement of summer rains in San Miguel de Allende, Mexico. He recounted that he had found a plant blooming in a garden trash pile about four years ago, and then took a cutting. The cutting formed a small rangy three-stemmed shrub about a metre in height. His plant now produces these buttercup yellow blooms, but David notes that like so many other cacti, the flowers only last a day.
In the email, David points out that it difficult to find anything written about this cactus species. He was right! This species is endemic to Mexico. It is distributed in the states of Jalisco, Colima, and Nayarit where it grows in tropical deciduous forests between elevations of 300-1800 metres. I also managed to dig up a bit about the evolution of the subfamily this species belongs to, the Opuntioideae.
The leafy habit of Pereskiopsis aquosa is curious, and the evolutionary history of leaf characters in the subfamily Opuntioideae is of interest (as well as below-ground storage morphology). This species-rich subfamily (the second most speciose subfamily in the Cactaceae with ~350 members) has a wide diversity of leaf and ground storage organ characters. Most genera in the subfamily possess early deciduous terete leaves that can be up to 2cm long, but are often much shorter. However, the genera Austrocylindropuntia, Quiabentia, and Pereskiopsis have persistent leaves. In addition to being described as distinctively persistent, the leaves of Pereskiopsis are flat, fleshy, ovate to spathulate, and up to 8cm long and 5cm wide.
The possession of persistent leaves within Opuntioideae, a family that is marked by stem-succulence, has given rise to some theorizing that the ancestral opuntioid was similar to either Austrocylindropuntia, Quiabentia, or Pereskiopsis. Others, however, have suggested that because of the reduced vasculature (transport tissue) in the persistent leaves within these genera relative to the relictual cactus leaves of earlier diverged Pereskia, that these persistent leaves are instead a derived character that actually represent an evolutionary reversal from within an ephemeral-leaved ancestral lineage. Based on the results of a character state reconstruction of ancestral leaf habit for the Opuntioideae, performed by researcher M. P. Griffith, the latter hypothesis is supported. His results showed that there were at least two derived independent adaptations of enlarged, persistent leaves in the Opuntioideae. Griffith explains that although most cacti possess a suite of morphological and anatomical adaptations for survival in arid regimes (such as stem-succulence), not all cacti may benefit. In areas where aridity is not the absolute limiting factor in growth (such as the habitats of Pereskiopsis, Quiabentia, and Austrocylindropuntia) increased surface area and photosynthetic capacity is actually adaptive.
Instead of Pereskiopsis, Quiabentia or Austrocylindropuntia representing the early morphology of Opuntioideae, Griffiths suggests that the early morphology of this subfamily may be best represented by the genus Maihueniopsis sensu lato (in the broad sense). The untenably monophyletic Maihenueniopsis is the deepest lineage within the Opuntioideae, and is characterized by being early deciduous, globular-stemmed, diminutive, and often geophytic. This genus, along with Puna, possess many characters that are plesiomorphic (ancestral) for the subfamily Opuntioideae. Some other hypotheses have suggested that the earliest Opuntioideae were true geophytes, though this remains unresolved. (see: Griffiths, M. P. (2009). Evolution of leaf and habit characters in Opuntioideae (Cactaceae): reconstruction of ancestral form. Bradleya. 27:49-58).