Dalmatian toadflax (Linaria dalmatica)

Synonyms: Linaria genistifolia subsp. dalmatica, Antirrhinum dalmaticum, Linaria macedonica

Common Names: Broadleaf Dalmatian toadflax

Description:

Dalmatian toadflax (Linaria dalmatica) is an invasive perennial from southeastern Europe and western Asia that was brought to North America as a garden flower and for making dye and medicine [1][4]. It has escaped to roadsides, pastures, and dry open ground, where it grows into dense patches of yellow snapdragon-like flowers that crowd out native plants and pasture grass [2][3]. MISIN tracks it because its deep, spreading roots and heavy seed production make it hard to remove once it settles in [2].

Habit:

Dalmatian toadflax is an upright perennial that grows up to about 4 feet tall, often in clumps of several smooth stems [2]. Its standout feature is the leaves: broad, heart-shaped, and waxy blue-green, each one clasping the stem where it attaches [2]. From late spring through early fall it carries spikes of bright yellow flowers shaped like snapdragons, each with an orange, hairy throat and a long spur pointing down from the back [2]. It is easiest to spot in summer, when the tall yellow flower spikes stand out along roadsides and in dry open fields [2]. The waxy, clasping leaves are the quickest way to tell it from its narrow-leaved cousin, yellow toadflax [2].

At-a-glance cues:

1. Broad, heart-shaped, waxy blue-green leaves that clasp the stem [2]
2. Bright yellow snapdragon-like flowers with an orange throat and a long spur, blooming late spring to early fall [2]
3. Upright clumps of smooth stems up to about 4 feet tall [2]
4. Grows on dry, sandy or gravelly ground ? roadsides, pastures, and open fields [2]

Leaves:

1. Arrangement: alternate, attached one at a time and clasping the stem [2]
2. Shape: broad, heart-shaped to egg-shaped, with a pointed tip [2]
3. Size: about 1 to 3 inches (2.5?7.5 cm) long [2]
4. Surface: waxy and smooth, blue-green [2]
5. Margin: smooth, without teeth [2]

Stems:

1. Habit: herbaceous perennial, with one to several upright stems from a woody base [2]
2. Height: up to about 4 feet (1.2 m) [2]
3. Surface: smooth and waxy, blue-green [2]
4. Base: stems rise from a deep taproot and spreading underground roots [2]

Flowers:

1. Color: bright yellow, with an orange, hairy bump in the throat [2]
2. Shape: snapdragon-like, with a long, thin spur pointing down from the back [2]
3. Arrangement: crowded along the upper stem in a spike [2]
4. Bloom time: May through September [2]
5. Sex: each flower has both male and female parts (perfect) [2]

Fruit and seeds:

1. Fruit type: a small, round, two-chambered capsule about 1/2 inch long [2]
2. Seed count: roughly 140 to 250 seeds per capsule, and a single plant carries many capsules [2]
3. Seeds: small; some are winged and blow in the wind, others spread in soil and water [2]
4. Ripening: capsules mature from summer into fall [2]
5. Spread: also spreads underground from creeping roots ? see Reproduction [2]

Habitat:

Dalmatian toadflax grows best on dry, well-drained ground with coarse, sandy, or gravelly soil [1][2]. It is native to southeastern Europe and western Asia and was introduced to North America, where it has spread across much of the western and northern United States and southern Canada [1]. It favors sunny, disturbed places ? roadsides, railroad edges, pastures, rangeland, gravel pits, and overgrazed or burned ground ? and shrugs off drought once its deep roots are set [2][3]. It is most troublesome in dry, open grasslands and forest openings [3].

Reproduction:

Dalmatian toadflax spreads two ways, which is what makes it so stubborn. It makes a huge amount of seed: each round capsule holds 140 to 250 seeds, and a single plant carries many capsules, so one plant can drop thousands of seeds in a season [2]. The seeds blow in the wind, wash downstream, and hitch rides in soil, gravel, hay, and on vehicles and equipment [2]. It also spreads underground ? a deep taproot reaches 6 feet or more, and side roots creep outward and send up new stems, so one plant becomes a patch [2]. Because a root piece left in the ground can grow into a new plant, moving soil from an infested spot can start a new patch [2]. Pulling plants before they flower and seed (by early summer) is the best way to slow it, but you must remove the roots too [2].

Impact and Damage:

Dalmatian toadflax is not a danger to people, but it is a problem for animals and for the land. Cattle and horses avoid eating it, partly because it contains mildly toxic compounds, so it spreads through pastures while the grass around it is grazed down [2]. On a property, it forms dense patches that crowd out garden plants, lawn, and native wildflowers [2].

In natural areas and on rangeland, it forms thick stands that push out native grasses and wildflowers and lower the variety of plants [2][5]. This hits grazing hard: grass production can be about two and a half times lower in dense toadflax stands than in nearby land without it, which means less forage for both livestock and wildlife [3]. Its deep roots and heavy seeding let it hold ground and keep spreading once it is established [3].

Similar species:

Dalmatian toadflax has yellow, snapdragon-like flowers that lead to a few mix-ups, but the leaves usually settle it.

Yellow toadflax (Linaria vulgaris), also called butter-and-eggs, is the closest look-alike and also invasive ? it has the same yellow, spurred snapdragon flowers, but its leaves are narrow and grass-like rather than the broad, waxy, clasping leaves of Dalmatian toadflax [2].

Garden snapdragon (Antirrhinum majus) has similar two-lipped flowers, but they come in many colors, lack the long backward spur, and the plant is a tidy garden flower rather than a spreading weed of dry open ground [2].

Monitoring and rapid response:

Signs to watch for:

1. Clumps of yellow snapdragon-like flowers on dry, open ground from late spring through early fall [2]
2. Broad, waxy, blue-green leaves that clasp smooth upright stems [2]
3. Round seed capsules along the upper stem in late summer and fall [2]

What you can do:

1. Pull or dig out plants before they flower (by early summer) to stop seed; the deep taproot and side roots resprout, so remove as much root as you can [2].
2. Bag any plants that already carry seed capsules and put them in the trash, so the seeds do not scatter [2].
3. Expect to return for several years ? buried seed and root pieces keep sprouting, so check the spot and pull regrowth each year [2].
4. Do not move soil from an infested area, since root fragments can start a new patch [2].
5. On larger sites, natural-area and rangeland crews clear scattered outlier patches first to slow the spread; in heavily infested western regions, land managers also release an introduced stem-mining weevil that weakens dense stands over time [5].

When to call a professional:

1. Large or well-established stands, or patches whose deep, creeping roots keep resprouting after repeated digging [2][3].
2. Infestations on rangeland or pasture, where the weed cuts into grazing [3].
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Linaria dalmatica (L.) Mill. (Dalmatian toadflax, symbol LIDA). plants.usda.gov
2. Minnesota Department of Natural Resources. Dalmatian toadflax (Linaria dalmatica). dnr.state.mn.us
3. Jacobs J, Sing SE (2006). Ecology and management of Dalmatian toadflax (Linaria dalmatica (L.) Mill.). USDA Forest Service / USDA NRCS Invasive Species Technical Note MT-3. research.fs.usda.gov
4. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. Linaria dalmatica (L.) Mill. powo.science.kew.org
5. California Invasive Plant Council (Cal-IPC). Linaria dalmatica ssp. dalmatica profile. cal-ipc.org

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