Alyssum desertorum
(desert madwort)

A. desertorum is an herbaceous plant native to central and eastern Europe, North Africa and Asia (from Turkey to Xinjiang in northwestern China). It has become naturalized in northern Europe as well as in western North America, where it is classed as an introduced species, a weed and a weak invader. A. desertorum is a weed predominately of disturbed areas such as overgrazed semiarid rangelands and areas affected by industrial activity. Its spread has been facilitated recently by the expansion of hydraulic fracturing ('fracking') of deep rock formations for methane or oil extraction. A. desertorum is an environmental threat mainly due to its displacement of native plant species, including a number of endangered species.

In Europe there is confusion about the status of A. desertorum in the Baltic States, with some sources claiming it to be native and others that it is an introduction. USDA-ARS (2015), for example, lists the species as being both native and naturalized in Latvia, Lithuania and Estonia.

The status of A. desertorum in Tibet is uncertain as it was not recorded in Flora Xizangica Vol. 2 (Wu, 1985) and it seems its presence is solely based on the holotype of A. desertorum var. himalayense collected in the 1830s in the Himalayas on the Tibet border.

In the USA, the Jepson Flora Project (2014) noted the presence of A. desertorum in disturbed areas and rocky sagebrush flats at an altitude of 1000–1500 m in California's Inner South Coast Ranges and Modoc Plateau, with the range extending to Washington and Nebraska. According to Johnson (1999) A. desertorum has been identified as an alien invasive in a number of national parks, including Yellowstone National Park (which is primarily located in Wyoming but also extends partially into Idaho and Montana), Bighorn Canyon National Recreation Area (in the northern Rockies of Wyoming and Montana), Devil's Tower National Monument (northeastern Wyoming), Little Bighorn National Battlefield Monument (Montana) and Wind Cave National Park (South Dakota). It is in Yellowstone National Park that much research into A. desertorum control has been undertaken.

According to Mosley (2014), writing about the situation in Montana, there is a perceived expansion in the range of A. desertorum with the species becoming more prevalent and problematic in the west, centre and south-east, although it is not listed as a noxious weed in the state. The reasons for the expansion in distribution are not clear, but climate change could be a cause, not only in Montana but throughout the western USA. Although there has been no research into the consequences of climate change per se on the spread of A. desertorum, recent serious droughts, for example, may have weakened established plant communities allowing invasion by Alyssum species which are more adapted to drought conditions. Mild winters favour A. desertorum seedling establishment and the adoption of reduced tillage of croplands by farmers may have encouraged the formation of environments more suitable for invasive species. Increased industrial activity, especially fracking, also favours the spread of A. desertorum by providing it with a suitable disturbed habitat to colonize. Seed of A. desertorum can adhere to both animals and vehicles and may be accidentally transported and introduced into new locations.

In its native range, A. desertorum is found from near sea level up to an altitude of around 2600 m. It prefers arid and semiarid lands, deserts and rocky areas (Flora of China, 2015). Grubov (2001) indicates that in Mongolia A. desertorum is found on steppes, stony and debris-covered slopes and alkaline waterside gravels. In Poland, A. desertorum was identified as a species characteristic of xeric sand grasslands (Matuszkiewicz, 2001).

In North America, it is found at altitudes of 800-2000 m, in deserts, rocky areas, prairies, around grain elevators, railway beds, disturbed sites, roadsides, fields, meadows and sagebrush flats (Mulligan, 2002; Flora of North America Editorial Committee, 2015). Dry, gravelly areas on rangelands and croplands are also favoured.

Genetics

A. desertorum has a chromosome number of n = 16 (Mulligan, 1964); 2n = 32 (Murín et al., 1999).

Reproductive Biology

A. desertorum is an annual forb that propagates by seed. With its coloured flowers, pollination is assumed to be entomophilous (FloraGREIF, 2010). Khan (2003) reports on the pollen morphology of seven Alyssum species, including A. desertorum, from Pakistan. Pollen grains are tricolpate with a reticulate tectum. Little variation between species was observed in shape, size, colpi length and exine pattern, but a palynological key to the species is provided. According to data collected in the Gurbantunggut Desert in northwest Xinjiang by Liu et al. (2014), seeds weigh 0.37 mg, are dispersed by rain drops (ombrohydrochory).

Physiology and Phenology

Plants flower in spring, with flowering, fruiting and seed dispersal occurring between March and July, depending on location. In North America plants flower and fruit from April to July, and from April to June in China. Plants die in summer after seed is shed. Seeds must after-ripen on the soil surface for several weeks before they can germinate. Most seeds will germinate in the current year. Germination rates of 93% have been recorded (Liu et al., 2014). Flowering and seed production are delayed following mild winters, allowing germination to occur in autumn when soil moisture is usually optimal for seedling survival. Although harsh winters promote early flowering and seed dispersal, seedling death is frequent under the subsequent hot, dry conditions of summer. The trichomes covering the plant that give it a greyish appearance help retain moisture, a feature typical of plants of arid and semiarid habitats.

Associations

In Poland, A. desertorum was identified as a species characteristic of xeric sand grasslands of the Koelerion glaucae [Koeleria glauca] complex and the association Cerastio-Androsacetum septentrionalis (Matuszkiewicz, 2001).

In western North America, it is invading big sagebrush (Artemisia tridentata) complexes (Bates et al., 2004).

Environmental Requirements

A. desertorum is found growing at altitudes from sea level to 2600 m in its native range and 800-2000 m in North America, its introduced range. A. desertorum is a temperate species which prefers free draining soil.

Erysiphe cruciferarum was observed in 2005 infecting leaves of A. desertorum and A. hirsutum growing on a farm near Ankara in central Turkey (Karakaya, 2006). The same disease had previously been reported on A. desertorum in 1926 in Romania (HerbIMI, 2015). In 1977 Peronospora parasitica [Hyaloperonospora parasitica] was also reported on A. desertorum in Romania (HerbIMI, 2015).

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Human food and beverage

• Oil/fat

Materials

• Oils

Medicinal, pharmaceutical

• Traditional/folklore

Presence of A. desertorum can be determined by visual inspection of plants and seeds.

Rew et al. (2007) in their survey of non-indigenous plant species, including A. desertorum, in the Northern Range of Yellowstone National Park in 2001-2004, surveyed along transects to allow data to be collected continuously and a large sample size to be generated. Surveying along transects allowed changes in underlying environmental variables to be recorded, which was important for estimating the geographic distribution of the species from the sample data. Transects established perpen­dicular to roads and trails were accepted as the most effective sampling methodology. At a length of 2000 m, transects were sufficiently long to cross a number of habitat types. Paired transects were used to maximize surveying time while in the field. Transects were walked and survey observations were made within a 10 m wide swath. Surveys over an area of 529,000 m x 10 m in the Park's Northern Range found A. desertorum to be one of nine species that were observed to occur over more than 1% of the surveyed area (Rew et al., 2007).

Commenting on introduced Alyssum species in the USA, Dudley (1968) noted that A. desertorum was often confused with but could be easily distinguished from the very similar A. alyssoides. A. desertorum is identifiable by its larger and glabrous silicles and early deciduous sepals; in A. alyssoides the silicles always possess an indumentum of stellate trichomes and the sepals are persistent. Both species grow on dry, gravelly areas on rangelands and croplands, but A. desertorum occupies harsher, rockier sites at lower elevations (Mosley, 2014).

Weeds mistaken for A. desertorum in Montana include hoary alyssum (Berteroa incana), a Priority 2A noxious weed in the state and whitetop (Lepidium draba) a Priority 2B noxious weed. B. incana is taller than A. desertorum with white flowers which bloom from May to September. L. draba is also taller than A. desertorum with white-flowers, but is also perennial and with leaves covered in straight rather than stellate trichomes (Mosley, 2014).

In the Tianshan Mountains of central Asia, A. desertorum is similar to Arabidopsis thaliana in terms of ecological requirements and habitats (Jacobs, 2012).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention

SPS Measures

As A. desertorum can be transported in hay, only certified weed-free hay is allowed in or through Yellowstone National Park (Olliff et al., 2001).

Cultural Control and Sanitary Measures

To eliminate A. desertorum seed from being transported in gravel, any gravel destined for use in Yellowstone National Park has to be from a source operating a weed management plan or has to be heated to 150°C (Olliff et al., 2001).

Control

Physical/Mechanical Control

A native grass restoration project in the northern boundary area of Yellowstone National Park north of Gardiner, Montana, found that applying prescribed burns in October significantly reduced A. desertorum numbers the year following the burns (Jacobs, 2012). However, Bates et al. (2004) found that burning of Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis) by wildfires substantially increased A. desertorum cover.

Chemical Control

A number of herbicides, including metsulfuron and glyphosate, are known to temporarily reduce populations of A. desertorum (Jacobs, 2012). In the Lower Muddy Creek Watershed in Wyoming, small plot treatments were started in 2009 with a variety of different chemicals and rates to test for the most efficient and cost-effective treatment. Preliminary results show a 75-90% reduction in A. desertorum cover, a 15-75% increase in grass cover and a 100% increase in bare ground after treatments (BLM Wyoming, 2014). Removal of A. desertorum in this area would improve or maintain the habitat for wildlife and livestock using the area.

IPM and Ecosystem Restoration

A pilot native plant community restoration project was undertaken in the Gardiner Basin of the Yellowstone National Park, USA in 2008-14. This project had an integrated approach to controlling A. desertorum. Treatments involved herbicide applications, hand pulling, burning, harrowing, construction of exclosures and planting a barley/wheat cover crop to stabilize the soil and stimulate soil biota. Preliminary results indicate that the management actions undertaken have increased the likelihood of long-term successful native vegetation restoration (Renkin et al., 2014). A vigorous native plant community can help prevent invasion of an area by weedy species (Olliff et al., 2001).

Research into the effects of climate change on A. desertorum is needed, as well as more assessments on the impact of fracking on native plant communities and alien plant invasions.

15/02/2015 Original text by:

Andrew Praciak, Carne, Wexford, Ireland.