Montana Field Guide

Rhizomatous perennial. Stems ascending to erect, 20–45 cm. Basal leaves lanceolate, 3–6 cm long, dentate. Stem leaves auriculate-clasping. Vestiture of sparse to dense, simple hairs. Flowers white; petals 2–4 mm long; stamens 6. Fruit obovoid, pubescent, rounded at the base, 2–4 mm long, not notched; style 0.5–1 mm long; pedicels 4–11 mm long, glabrous (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

There are many white-flowered species in the Mustard Family, both native and exotic. It is recommended that identifications be made using a plant manual designed for Montana. Mustards have flowers with 4 sepals, 4 petals, and 6 stamens (4 long and 2 short) among other characteristics.

Globe-podded Whitetop – Lepidium appelianum, exotic:
* White-flowered plants that grow from creeping roots (rhizomes) and have mature silicles (fruits) that are not notched at their tip.
* Silicles are pubescent (have hairs), inflated (globe-shaped), and with a short style of 0.4-1.0 mm long. Silicle stems (pedicels) are 4-11 mm long.
* Stem leaves are auriculate (lobed like an arrow) and clasping around the stem.

Perennial Pepperweed – Lepidium latifolium, exotic and Noxious:
* White-flowered plants that grow from creeping roots (rhizomes) and have mature silicles (fruits) that are not notched at their tip.
* Silicles are glabrous or sparsely pilose (long soft hairs) with a very short style of 0.1 mm long or less. Silicle stems (pedicels) are 2-5 mm long.
* Stem leaves are sessile, but do not clasp around the stem.

Whitetop – Lepidium draba, exotic and Noxious:
* White-flowered plants that grow from creeping roots (rhizomes) and have mature silicles (fruits) that are not notched at their tip.
* Silicles are glabrous (lack hairs), flattened, and their base is cordate (heart-shaped or indented). Silicles are tipped with a style of 1-1.5 mm long. Silicle stems (pedicels) are 5-12 mm long.
* Stem leaves are auriculate (lobed like an arrow) and clasping around the stem.

Lenspod Whitetop – Lepidium chalepense, exotic:
* White-flowered plants that grow from creeping roots (rhizomes) and have mature silicles (fruits) that are not notched at their tip.
* Silicles are glabrous (lack hairs), partially inflated and round (compressed-globose), not cordate (is pointed to its stem), and topped with a style 1-2 mm long. Silicle stems (pedicels) are 8-15 mm long.
* Stem leaves are auriculate (lobed like an arrow) and clasping around the stem.

The other Montana Lepidium species (using MTNHP preferred name) have mature silicles with a notch of at least 0.1 mm deep at their top and are not rhizomatous.

Hoary False-alyssum – Berteroa incana, exotic and Noxious:
* White-flowered, annual plants that grow from taproots and have mature silicles (fruits) that are not notched at their tip.
* Each of the 4 petals are notched, making the flower appear 8-petaled.
* Plants have star-shaped hairs; whereas, Lepidium species have simple hairs or none.
* Stem leaves are widest near their tip (oblanceolate), sessile on the stem, and point upwards.

Field Pennycress – Thlaspi arvense, exotic:
* Easily differentiated if in fruit and easily confused with other species if only of leaves.
* White-flowered, annual plants that grow from taproots and have mature silicles (fruits) that are large, deeply notched at their tip, flat, and with wide wings, resembling a penny.
* Lower stem leaves have petioles. Upper stem leaves are sessile, clasping, auriculate (lobed like an arrow), and with smooth to toothed margins.

Common Yarrow – Achillea millifolium, native and desirable:
* Member of the Aster/Sunflower Family.
* Bright-white flowers arranged closely in a flat-topped inflorescence.
* Leaves are 2-3 times pinnately dissected, appearing fern-like or bushy like a squirrel’s tail.

Sources: Jacobs and Mangold 2007; FNA 2010; Graves-Medley and Mangold 2011; Lesica et al. 2012.

Agricultural fields, roadsides; plains, valleys (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Useful Links:
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage.
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides