Thank you to dinesh_valke@Flickr of Thane, India, for contributing today's photograph (original via the BPotD Flickr Pool). I've an ulterior motive for selecting one of Dinesh's photographs today -- I also wanted to thank him for figuring out an identification mystery over at the Human Flower Project weblog: Don't Forget to Check the Swamp.
Dinesh pointed out in the text accompanying his Flickr upload that Strobilanthes callosus "blooms only once in seven years", and that seemed worthy of some investigation. It turns out that some species of Strobilanthes are examples of a phenomenon termed masting. Masting can be defined as "synchronous production of seed at long intervals by a population of plants" (ref: Janzen (1976) in Annul. Rev. Ecol. Syst., 7, 347-391). I've commonly associated this with bamboo (see Bamboo, Rats and Famine) and did not know it also occurred in Strobilanthes. Being even more specific, both bamboo and Strobilanthes can be examples of strict masting, with "bimodal seed output with no overlap between the tails" and "masting species and mast years can be unambiguously identified" (from the Kelly reference below). This is opposed to other types of masting where the lines are blurry, for example, where every fifth year in a population is statistically more likely to be more productive than the other four, but there is still fruit production in all years or it may turn out not be more productive. It also needs to be noted that strict masting only occurs in species that are monocarpic (or semelparous) -- individuals of the species only reproduce once during a lifetime, then die.
Dave Kelly provides an overview of the phenomenon of masting in Kelly, D. 1994. The evolutionary ecology of mast seeding (PDF). Trends Ecol. Evol.. 9(12): 465-470. Kelly reviews the eight hypotheses that have been suggested to answer the question, "What factors most favour masting?": wind pollination, predator satiation, environmental prediction, resource matching, animal pollination, animal dispersal, accessory costs and large seed size. I wasn't able to determine the favourable factors for Strobilanthes callosus to exhibit this behaviour, but it can perhaps be inferred from a study on Strobilanthes kunthianus: Sharma, MV et al. 2008. Reproductive strategies of Strobilanthes kunthianus, an endemic, semelparous species in southern Western Ghats, India. Botanical Journal of the Linnean Society. 157:155-163. DOI: 10.1111/j.1095-8339.2008.00786.x.
In the paper by Sharma et al., they suggest that animal pollination and the "evolution of the adaptive floral traits has facilitated mast seeding in the species", i.e., floral traits which result in 100% pollination efficiency. "As semelparous plants have only one chance to reproduce, they are expected to develop effective strategies to prevent reproductive failure".
Strobilanthes callosus is endemic to India, and its Hindi common name is karvy.
Photography resource link: I recall positively reviewing and linking to Radiant Vista some time ago (in part due its daily image critiques), but that site is now defunct and some of the people behind the site seem to be pursuing individual ventures. One to investigate, where the daily image critiques are still available (but now require free registration), is The Mindful Eye. One of the main people behind this new site is photographer Craig Tanner.