Trillium petiolatum Pursh

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Trillium petiolatum, the Idaho trillium, also known as the long-petioled trillium or round-leaved trillium, is a species of flowering plant in the family Melanthiaceae. It is native to the northwestern United States, in Idaho, Oregon, and Washington. Its type specimen was gathered by Meriwether Lewis during the return trip of the Lewis and Clark Expedition in 1806.

Description

Trillium petiolatum is "without question the least Trillium-like of all trilliums." The specific epithet petiolatum, meaning "petioled," is intended to draw attention to its very long petioles, which are 5 to 12 cm (2 to 5 in) long. The petioles are nearly as long as the leaf blades, which themselves are 7 to 14 cm (3 to 6 in) long and 5.5 to 10.2 cm (2 to 4 in) wide. The round-ovate blades are green but not mottled. The petiolate leaves strongly resemble the leaves of the common plantain. Pursh himself observed that T. petiolatum "has leaves very much like Plantago major."

The scape is 4 to 17 cm (2 to 7 in) long but most of it remains below the surface since the rhizome is deep underground, presumably for protection. Consequently the leaf-whorl and the sessile flower sit at or near ground level. The flower is small, with sepals from 22 to 47 mm (0.87 to 1.85 in) long and 7 to 10 mm (0.28 to 0.39 in) wide and petals from 30 to 55 mm (1.2 to 2.2 in) long and 4 to 10 mm (0.16 to 0.39 in) wide. The petals are red, maroon, or purple, but yellow-flowered forms devoid of purple pigments have been identified. Due to its small size and uncharacteristic leaf structure (for a trillium), the plant is inconspicuous and easily overlooked.

Trillium petiolatum shows similarities to both T. sessile and T. recurvatum. Of the sessile trilliums, only T. recurvatum and T. petiolatum have petiolate leaves, but apart from this, the two species have little else in common. Based on flower parts and reproductive organs, T. petiolatum appears to be more closely related to T. sessile.

Trillium petiolatum - Wikipedia

 

wtu030465 (Trillium petiolatum) - Burke Herbarium Image Collection