This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Annual (or perennial?) herbs, with large long-petioled basal leaves, erect simple scapes and terminal panicled spikes of bracted usually purple flowers. Sepals 3, membranous, separate, equal. Petals 3, separate or somewhat coherent at the base. Staminodia slightly united below, one of them (labellum) broad, crested. Anther i-celled. Ovary 1-celled or with 2 additional small empty cavities. Base of the style adnate to the base of the stamen-tube. Stigma 2-lipped, dorsally appendaged. Capsule globose of ovoid. Seed erect. Embryo strongly curved. [In honor of Johann Thalius, German naturalist of the sixteenth century.]
Plant finely white-powdery nearly all over. Scapes rather stout, terete, 3°-6° tall; petioles \°-2\° long, terete; leaves ovate-lanceolate, acute or acuminate at the apex, rounded, narrowed or subcordate at the base, 1/2°-1° long, 3'- 5' wide; panicle 8'-18' long, its spikes numerous, usually erect or ascending; bracts of the panicle narrow, deciduous, not longer than the spikes; bractlets ovate, unequal, coriaceous, about ¥ long; flowers purple, longer than the bractlets; capsule ovoid, about 4" in diameter.