Today's photographs and write-up are courtesy of Ian Gillam, one of UBC Botanical Garden's many exceptional Friends of the Garden. Thank you! Ian writes:
Erodium trifolium is a member of the Geraniaceae native to North Africa. Like many plants of the region it grows in winter, flowers in early spring and is largely dormant in summer drought.
In Vancouver, Erodium trifolium is reasonably hardy outdoors in a well-drained and sheltered area, such as close to the south side of a house. In exceptionally cold winters plants may be damaged or killed.
In common with the related genera Geranium and Pelargonium, successfully pollinated flowers of Erodium produce a lengthening style from the centre of their flowers, growing to about 2.5 cm in this species. As this rostrum develops, the flower heads take on a fanciful resemblance to the heads of long-beaked birds. Botanical names of Geranium, Pelargonium and Erodium derive from Greek names of crane, stork and heron, respectively. Their common names also refer to these birds' long bills. As the seeds mature, the fruiting body turns brown and dries. The ovary splits into five segments, termed mericarps, each containing a single seed. Each mericarp is attached to a tail, an awn, that curls up to pull away from the rostrum.
As Erodium trifolium awns dry, the lower parts coil into tight helices of about five turns, leaving a terminal section curved but uncoiled. A single mericarp is shown above.
The pointed tip has a slight hook and many short, backward-pointing bristles. These features may help mericarps attach and penetrate into fur or feathers, possibly aiding distribution of seeds. Mericarps fall to the ground with the heavier end first. With luck the tip may lodge in some slight crack in the soil. The awn is sensitive to moisture and a slight wetting, even by dew, causes it to unwind within minutes. If the protruding tail catches on a piece of gravel or a plant's stem the power of the unwinding is transferred to the mericarp, thrusting it forward and screwing it into the ground (with a left-hand thread). Should the attempt fail, the sun's warmth will soon cause the awn to coil again and wind may move the whole to a better location for another try at planting.