ePostcard #37: Megaherb Mysteries

Botanists continue to be puzzled by the prevalence of outsized leaves and flowers—the so-called megaherb flora—of the subantarctic islands. It is not known whether the megaherbs are relics of an ancient, more widespread flora that pre-dates the Ice Ages or whether the flora evolved in isolation on the islands themselves. What we do know is that there are at least 10 taxa endemic to these islands, and they occur in four genera: Anisotome, Bulbinella, Pleurophyllum and Stilbocarpa. Several theories have been proposed to explain the megaherb flora and why it has become such an integral part of these unique island plant communities. Some botanists have suggested that the large leaves are an adaptation to cloudy, humid conditions and cool temperatures. If you look closely at the corrugated leaves in photo #6 (Pleurophyllum speciosum), you will note a dense coating of fine hairs on the ridges of the corrugations. An increase in leaf surface temperature of up to 15 degrees Celsius has been recorded in these corrugated leaves in contrast to large smooth leaves on adjacent plants. It has also been suggested that the bright and intensely colored flowers of the megaherbs would absorb more diluted sunlight than lighter colors would, and would undoubtedly attract pollinators and allow fertilization and seed development to proceed more rapidly during the short summer season.

Key to the Photos

Header Image above:
#1 Bulbinella rossii (Ross Lily; yellow) & Anisotome latifolia (Campbell Island Carrot; dark rose)

Images Below:
# 2 New Zealand Fur Seal (about to enjoy a private mud wallow in the lilies)
# 3 Pleurophyllum hookeri (Lance-leaf Button Daisy; only flowers en masse every 2-3 years)
#4 Red-crowned Parakeet (surprised while foraging on the succulent flower buds of the Macquarie cabbage)
#5 Macquarie Island Cabbage
#6 Pleurophyllum speciosum (daisy family)
#7 Gentiana cerina (Giant Gentian; grows as an enormous cushion plant)

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