Jefferson's Twinleaf

Description

Jeffersonia diphylla, often called "Jefferson's twinleaf", is the name of a rare plant species found in Wauwatosa. Jeffersonia diphylla is the only confirmed species of its genus in existence. The only other plant of the same genus, which is unconfirmed, is the Jeffersonia dubia, which is only found in China, Russia, and Europe. The leaves and flowers of this plant are smooth and emerge directly from the rhizome at base of the plant. Jeffersonia has showy white flowers with eight petals; the flower resembles Bloodroot. The short-lived flower appears in April or May, before the forest canopy appears (see spring emphemeral). The fruit is a green pear-shaped capsule with a hinged top. The characteristic leaves are large and nearly divided in half, giving rise to its common name, twinleaf. Plants in this genus rarely grow taller than 12 inches (30 cm). As with many other deciduous forest plants, the seeds are dispersed by ants, a process known as myrmecochory. The twinleaf is considered rare throughout its range, which is the eastern part of North American. Wisconsin is at the northwest limit of the twinleaf range, which is why it is especially rare here. And of the three known occurrences of the twinleaf in Milwaukee County, all are in Wauwatosa. It is found only in highly calcareous soils, or those containing calcium carbonate. In Wauwatosa and elsewhere in Wisconsin – the twinleaf is found in our state only in counties bordering Lake Michigan – the soil is calcareous because of limestone bedrock that is the residue of an ancient Silurian sea. Curiously, the Jefferson's twinleaf belongs to a genus comprised of but two species; the other occurring only in China. How the two very closely related species, with no other near relatives, ended up almost exactly half a world apart, is unknown.