Descurainia spp., tansy mustard
Herbaceous

Descurainia spp.

tansy mustard

Brassicaceae

Variable by species; D. sophia native to Eurasia; D. pinnata native to western North America

At a Glance

TypeAnnual
HabitUpright
FoliageDeciduous
Height12-36 inches (30-90 cm)
Width6-18 inches (15-45 cm)

Key Features

Attracts Pollinators
Drought Tolerant
Maintenancemoderate

Overview

Descurainia spp. (tansy mustards) are winter annuals or biennials in the mustard family (Brassicaceae) reaching 12–36 inches (30–90 cm) tall with a 6–18 inch (15–45 cm) spread. The genus includes both introduced species such as D. sophia (flixweed) and native species such as D. pinnata (western tansy mustard). Plants form a basal rosette of finely 2–3 times pinnately dissected leaves 2–5 inches (5–13 cm) long, gray-green, covered in fine stellate (star-shaped) hairs. Flowering stems are erect, branching in the upper half, with progressively smaller, finely divided leaves. Flowers are small, pale yellow, four-petaled, 0.08–0.12 inch (2–3 mm) across, borne in terminal racemes. Fruit is a slender, ascending silique 0.4–1 inch (10–25 mm) long, depending on species. D. sophia produces siliques 0.6–1 inch (15–25 mm) long containing 20–40 tiny reddish-brown seeds; a single plant produces 10,000–100,000 seeds. Seeds contain glucosinolates and can accumulate toxic levels of nitrates and sulfur compounds; livestock ingestion of large quantities causes pulmonary emphysema and blindness in cattle (a condition called polioencephalomalacia). Fall-germinating seedlings overwinter as rosettes and bolt in spring.

Native Range

The genus Descurainia includes both native and introduced species in North America. D. sophia (flixweed) is native to Eurasia and northern Africa, now widely naturalized across North America in disturbed, dry sites from sea level to approximately 8,500 feet (2,600 m). D. pinnata (western tansy mustard) is native to western North America. Both species occur in the Pacific Northwest in rangeland, roadsides, cultivated fields, and waste areas.

Suggested Uses

Used in rangeland weed identification and livestock toxicology training. Studied in dryland weed ecology and Brassicaceae taxonomy courses. Native Descurainia species are host plants for the sara orangetip butterfly (Anthocharis sara) and other pierid butterflies in western North America.

How to Identify

Identified by the finely 2–3 times pinnately dissected leaves with very narrow segments, giving a feathery, tansy-like appearance, and the covering of fine stellate hairs (visible under hand lens). Distinguished from Sisymbrium species (tumble mustards) by the more finely divided leaves and shorter siliques. D. sophia is distinguished from the native D. pinnata by the longer siliques 0.6–1 inch (15–25 mm) versus 0.3–0.5 inch (8–12 mm), and by having more seeds per silique (20–40 versus 4–12). Flowers are very small, 0.08–0.12 inch (2–3 mm) across.

Appearance

Size & Dimensions

Height1' - 3'
Width/Spread6" - 1'6"

Colors

Flower Colors

yellow

Foliage Colors

green
gray

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~6 weeks
J
F
M
A
M
J
J
A
S
O
N
D
SpringSummer
Flowers from April through July. Individual racemes bloom over 2–3 weeks, with flowers opening from the bottom upward. Peak bloom in the Pacific Northwest occurs in May through June. Seeds mature 3–4 weeks after pollination. Self-pollinating. Siliques are indehiscent or weakly dehiscent, releasing seeds near the parent plant.

Detailed Descriptions

Flower Description

Yellow

Foliage Description

Gray-green to green, finely 2-3 times pinnately dissected with narrow segments, covered in fine stellate (star-shaped) hairs

Growing Conditions

Sun Requirements

Full Sun
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 8.5(Neutral)
357912
Soil Types
sandloamsiltrocky
Drainage
well drained

Water & Climate

Water Needs

Very Low

Frost Tolerance

hardy

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Management focuses on removal before seed maturity, as the high seed output (10,000–100,000 per plant in D. sophia) replenishes the soil seed bank rapidly. Fall-germinating rosettes are hand-pulled or hoed in late winter through early spring before bolting. Plants pull easily from loose, dry soils due to a shallow taproot. Mowing at early bloom prevents seed set. Dense mulching or competitive cover crops suppress germination on disturbed sites. Livestock should not graze dense stands, as accumulated glucosinolates and sulfur compounds cause livestock toxicity when consumed in quantity. Seeds germinate primarily in fall with secondary flushes in spring.

Pruning

No pruning applicable. Plants are removed by pulling or hoeing before siliques mature. Cutting at ground level during early flowering prevents seed production. The annual or winter annual life cycle means plants do not resprout from roots after complete removal.

Maintenance Level

moderate

⚠️ Toxicity Warning

Toxic to pets