Montana Field Guide

PLANTS: Biennial or short-lived perennial herbs, 25-60 cm tall, and glabrous (lack hairs) to sparsely pubescent. Stems grow branched and erect. Sources: Al-Shehbaz in FNA 2010; Lesica et al. 2012.

LEAVES: Basal and stem leaves present, and often glaucous. Basal leaves whither by flowering time. Basal leaf petioles, ciliate, and 2-4 cm long. Basal leaf blades are 2-10 cm long, lanceolate to obovate in shape, and with entire (smooth) margins. Stem leaves are alternately arranged, sessile (lack petiole), auriculate where they clasp the stem, lanceolate to linear-lanceolate in shape, 15-30 cm long, and with entire margins. Sources: Al-Shehbaz in FNA 2010; Lesica et al. 2012.

INFLORESCENCE: A densely flowered raceme that lacks bracts and is terminal on the plant (but does not elongate in fruit). Flowers are lavender to purple. Sepals are erect, ovate to oblong-ovate, (3-) 3.5-5 (-6) mm long by (1-) 1.5-2mm wide. Petals are lavendar to purple, spatulate to broadly obovate in shape, (6.5-) 8-11.5 (-14) mm long by 2.5-5 (-6) mm wide, and margins are not crisped. Petal's claw is slender, narrowest at its base, and strongly differentiated from the blade, (2-) 2.5-4 (-5) mm. Fruit is an erect, linear silique with a short stipe, slightly torulose, and constricted between the seeds. Sources: Al-Shehbaz in FNA 2010; Lesica et al. 2012.

Thelypodium comes from the Greek words of thelys meaning 'female' and podoin meaning 'little foot' and refers to the stipitate ovary that many species in this genus have.

Flowering from June to July (Al-Shehbaz in FNA 2010).

Differentiating Montana's three Thelypodium species requires a technical key, such as those by AL-Shehbaz in FNA 2010, Lesica et al (2012), and Giblin et al. [eds.] 2018. Other genera can also appear similar. Thelypodium species have cylindrical siliques while species of Arabis have flattened siliques.

Northwestern Thelypody - Thelypodium paniculatum, SOC
* Stem Leaf: Auriculate-clasping, mostly sessile.
* Inflorescence: Terminal racemes do not considerably elongate in fruit (opened flowers crowded at tip).
* Flower: Petals lavender to purple, 2.5-5 mm wide. Anthers 1-2 mm long.
* Fruit: Siliques often straight, 1.3-2.3 mm wide.
* Seed: Plump.
* Habitat: Wet meadows and streambanks. In the montane zone of Montana.

Slender Thelypody - Thelypodium sagittatum subspecies sagittatum, SOC
* Stem Leaf: Auriculate-clasping, mostly sessile.
* Inflorescence: Terminal racemes do not considerably elongate in fruit (opened flowers crowded at tip).
* Flowers: Petals light to deep violet-purple, 1-3 mm wide. Anthers 2-3 mm long.
* Fruit: Siliques often straight, 0.5-1.2 mm wide.
* Seeds: Flat.
* Habitat: Moist, often alkaline meadows that dry by summer, desert plains to lower mountains. In the montane zone of Montana.

Entire-leaved Thelypody - Thelypodium integrifolium subspecies integrifolium
* Stem Leaf: Bases are cuneate to attenuate, not auriculate, sagittate, or auriculate clasping; sessile.
* Flower: Petals white to purple, 4-7 mm wide
* Fruit: Siliques ascend, 1-3 cm by 0.7-1.1 mm long with a 0.3-2.0 mm long stipe.
* Habitat: Moist to wet, alkaline or saline meadows in the plains, valleys, and montane zones of Montana.

Northwestern Thelypody occurs in the Montane zone of Montana (Lesica et al. 2012). Plants grow in wet sedge meadows where the water level may cover basal portions of the plant. It appears to favor meadows and stream bottoms that remain wet for most of the season.

Plants reproduce by seed.

FLOWERS
A densely flowered raceme that lacks bracts and is terminal on the plant. At anthesis, open flowers are crowed at the tip of the inflorescence.
* Sepals are erect, ovate to oblong-ovate, (3-) 3.5-5 (-6) mm long by (1-) 1.5-2mm wide.
* Petals are lavendar to purple, spatulate to broadly obovate in shape, (6.5-) 8-11.5 (-14) mm long by 2.5-5 (-6) mm wide, and margins are not crisped. Petal claws are slender, narrowest at their base, and strongly differentiated from the blade, (2-) 2.5-4 (-5) mm.
* Anthers are 1-2 mm long.

FRUITS
Fruit is an erect, linear silique with a short stipe, slightly torulose, and constricted between the seeds. Siliques are (1-)1.5-2.5 mm wide.

SEED DISPERSAL
Northwestern Thelypody has lightweight seeds that are probably very easily distributed (Al-Shehbaz 1973). Wind may be an important factor in their dispersal in open habitats such as deserts, flats, and open slopes, but the action of rain wash is perhaps as equally important, if not more important (Al-Shehbaz 1973). Flooding is likely a major means of seed dispersal for species found along streams and riverbanks and in creek beds, and may also be an important vector for plants growing in meadows (Al-Shehbaz 1973).

STATE THREAT SCORE REASON
Reported threats to Montana's populations of Northwestern Thelypody are currently assigned as Unknown (MTNHP Threat Assessment 2021). Northwestern Thelypody could be vulnerable to riparian grazing or hydrologic changes based on a current, but a limited understanding of its life history and habitat requirements.