Synonym(s): Linaria genistifolia
Family: Plantaginaceae (formerly Scrophulariaceae)
Duration and Habit: Perennial Forb/Herb
(From Wilson et al. 2005)
Erect herb with one to 25 stiff, vertical, leafy stems that are thick-walled, fibrous, and waxy in appearance. Mature Dalmatian toad-flax plants grow 2 to 5 ft (0.8 to 1.5 m) tall. Nonflowering, prostrate stems are produced in the summer and usually persist until the following growing season. Leaves are broad, alternate, 1 to 2 in (2 to 5 cm) long, and almost as wide. The lower leaves are heart-shaped and clasp the stem; upper leaves are smaller and ovate-lanceolate shaped. Leaves are usually bluish-green and have a distinct waxy appearance.
The Dalmatian toadflax flower is a bright yellow, two-lipped, snapdragon-like blossom with an orange throat and a long spur. Flowers are borne on short stalks that arise in the axils of upper stem leaves, and are 0.8 to 1.6 in (2 to 4 cm) long.
Dalmatian toadflax produces egg-shaped to nearly round, upright seed capsules that are 0.2 to 0.4 in (0.4 to 1.0 cm) long and 0.2 to 0.3 in (0.4 to 0.9 cm) wide. Each capsule contains 60 to 300 seeds. Seeds are sharply triangular, slightly winged, and approximately 0.04 in (0.1 cm) long.
Note: Dalmatian toadflax can sometimes be found in the literature referred to botanically as L. genistifolia or L. genistifolia ssp. dalmatica. This is because the taxonomy of Dalmatian toadflax and its various biotypes or hybrids are not clearly understood. Although it is difficult to assign a definitive name to invasive Dalmatian toadflax, it is important to understand that, because hybrids occur, toadflax exists in a variety of forms.
Native Lookalikes: Currently no information available here yet, or there are no native Texas species that could be confused with Dalmatian toadflax.
Ecological Threat: Once established, high seed production and vegetative propagation enables Dalmatian toadflax to spread rapidly and to dominate and persist at a site. The large, contorted, deeply penetrating taproots and vigorous, early season growth enables Dalmatian toadflax to efficiently capture water and nutrients, outcompeting other plants in coarse, nutrient-poor soils (Wilson et al. 2005).
Biology & Spread: By seeds and vegetatively by adventitious stems from primary and lateral roots. This “can occur as early as two to three weeks after germination. Over time, these shoots form roots and eventually become independent plants. New shoots also can arise from severed root fragments as short as 0.4 in (1 cm) in length” (Wilson et al. 2005).
Biology and Ecology (From Wilson et al. 2005)
Seeds of Dalmatian toadflax germinate in the fall or spring. Seedlings grow quickly, establishing a deep, 20 in (51 cm) long taproot within eight weeks and producing two to five vertical flowering, and prostrate, nonflowering stems in the first season (Fig. 8b) . The prostrate stems grow in summer and remain green throughout the winter, especially under snow cover. In the second year and subsequent years, there can be up to 25 flowering stems and up to 40 nonflowering stems arranged a loose rosette at the base of the plant. Seasonal growth of stems can begin as early as February in warm areas, or as late as April in cooler, northern areas. Flowering occurs from May to October. Dalmatian toadflax is self-incompatible and must receive pollen from another toadflax plant in order to set viable seed. Flowers are cross-pollinated by bumblebees and other large bees, and seeds are produced from late June to December. A mature plant can produce up to 500,000 seeds, which are gradually released from the seed capsules through the fall and winter. Seeds can also be dispersed when stems break off and are blown around by the wind. Seed germination rates can be high, but seeds also can remain dormant in the soil for up to 10 years.
In addition to seeds, Dalmatian toadflax reproduces vegetatively by stems that develop from adventitious buds on primary and creeping lateral roots. Vegetative reproduction from root buds can occur as early as two to three weeks after germination. Over time, these shoots form roots and eventually become independent plants. New shoots also can arise from severed root fragments as short as 0.4 in (1 cm) in length.
Once established, high seed production and vegetative propagation enables Dalmatian toadflax to spread rapidly and to dominate and persist at a site. The large, contorted, deeply penetrating taproots and vigorous, early season growth enables Dalmatian toadflax to efficiently capture water and nutrients, outcompeting other plants in coarse, nutrient-poor soils. Lateral roots can grow up to 10 ft (3m) long, solidly anchoring the plant against anyone or anything attempting to dislodge it. Dalmatian toadflax roots have a lifespan of about four years.
Stems of Dalmatian toadflax contain an acrid, bitter-tasting liquid that makes the plant unpalatable to grazing animals. These compounds, called glycosides, are considered toxic to livestock, but reports of animal poisonings have not been reported [probably because livestock avoid the unpalatable plants].
History: It was brought to North America in the early 1900s for ornamental and medicinal purposes (Wilson et al. 2005).
U.S. Habitat: “Found in semi-arid areas on coarse-textured, gravelly soils. It is usually associated with sparsely vegetated areas, such as roadsides, abandoned or unmanaged land, gravel pits, and disturbed pastures and rangelands” (Wilson et al. 2005).
U.S. Nativity: Non-native
Native Origin: Eurasia
U.S. Present: AR, AZ, CA, CO, CT, IA, ID, IL, IN, KS, MA, ME, MI, MN, MT, ND, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SD, UT, VT, WA, WI, WY
Distribution in Texas: For distribution by counties in U.S., see http://www.swcoloradowildflowers.com/Yellow%20Enlarged%20Photo%20Pages/linaria.htm. Scroll to bottom of page. [Accessed Dec. 5, 2014]
The flower resembles that of Yellow Toadflax (Linaria vulgaris), but yellow toadflax has long, thin leaves instead of the broad leaves of Dalmatian Toadflax.
The best way to manage toadflax is to prevent it from establishing. This means vigilant monitoring of disturbed areas, especially if they are near established toadflax populations. Keeping the native plant community healthy goes a long way to preventing toadflax from establishing as the seedlings are poor competitors.
Physical: Can pull by hand, or mow, but any remnant roots will re-sprout. Discing/plowing is not recommended as it can leave root remnants as well as drag them to new places in fields. Mowing/cutting as plants begin to flower can prevent seed production, and repeated mowing/cutting over several years can deplete the stores in the deep tap roots; this is lily infeasible, especially in a natural/native plant area. Tilling can kill seedlings, but again, this is likely to be infeasible in natural areas.
Fire will not kill Dalmatian toadflax, as it will sprout from the surviving deep roots. Seeds can survive in the seed bank, but no studies have been done on the effects of fire on seeds. Fire may even aid the dominance of toadflax by removing competition (Zouhar 2003).
Chemical: Minnesota DNR suggests using herbicide with 2,4D, but may require repeated application, especially if there is a good seed bank (Chayka 2014).
Zouhar (2003) provides extensive discussion of the use of herbicides (http://www.fs.fed.us/database/feis/plants/forb/linspp/all.html#IMPACTS%20AND%20CONTROL). Picloram appears to be the most effective, but it kills non-target plants and does not provide complete control. “Permanent, long-term control of toadflax cannot be achieved with herbicide treatment alone” (Zouhar 2003). Use of herbicides that kill other plants can lead to a reduction of competition and therefore an increase in toadflax.
Biological: See Wilson et al. (2005) for a complete guide to using biological control. They discuss 7 species of insect that can help to control Yellow and Dalmatian Toadflax: Toadflax flower-feeding beetle (Brachypterolus pulicarius), Toadflax defoliating moth (Calophasia lunula), Toadflax root-boring moth (Eteobalea intermediella), Yellow toadflax root-boring moth (E. serratella), Toadflax stem-mining weevil (Mecinus janthinus), Toadflax seed-feeding weevils (Rhinusa antirrhini* and R. neta*), and Toadflax root-galling weevil (Rhinusa linariae*) [* formerly Gymnetron].
Cattle avoid yellow toadflax due to its containing several secondary compounds such as glycosides (Zouhar 2003). Goats have been used to control Dalmatian toadflax, but yellow toadflax appears to be unpalatable.
Wilson, L. M., S. E. Sing, G. L. Piper, R. W. Hansen, R. De Clerck- Floate, D. K. MacKinnon, and C. Randall. 2005. Biology and Biological Control of Dalmatian and Yellow Toadflax. USDA Forest Service, FHTET-05-13. [http://www.invasive.org/weedcd/pdfs/ToadflaxBook.pdf Accessed 2014, November 5]
Olmstead, Richard G., Claude W. dePamphilis, Andrea D. Wolfe, Nelson D. Young, Wayne J. Elisons and Patrick A. Reeves. 2001. Disintegration of the Scrophulariaceae. Am. J. Bot. vol. 88 no. 2 348-361 [Accessed 2014, November 5]
Zouhar, Kris. 2003. Linaria spp. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/plants/forb/linspp/all.html [2014, November 5].
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