Two useful terms

Laboring on the WWI (Weeds, Wildflowers, and Invasives) detail yesterday, I came across two useful technical terms in this domain. The concepts were long familiar to me, but the terminology was new: the adjective and noun ruderal; the adjective allelopathic and noun allelopathy.

ruderal. From NOAD2: Botany adjective  (of a plant) growing on waste ground or among refuse; noun  a plant growing on waste ground or among refuse. ORIGIN mid 19th cent.: from modern Latin ruderalis, from Latin rudera, plural of rudus ‘rubble.’

On waste ground, in disturbed places. Roadsides, by railroad tracks, at the edges of fields, in dumps, and so on. Prime location for many weeds and invasives. See, in my Penstemon posting, #4 (Plantago major) and #5 (Scrophularia nodosa).

allelopathic / allelopathy. From Wikipedia: Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms.

Though the term has wider applicability (in plant defenses against herbivores, for example),

Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of many invasive plants. For specific examples, see spotted knapweed (Centaurea maculosa), garlic mustard (Alliaria petiolata), Casuarina/Allocasuarina spp., and nutsedge.

… Allelopathy has been shown to play a crucial role in forests, influencing the composition of the vegetation growth, and also provides an explanation for the patterns of forest regeneration. The black walnut (Juglans nigra) produces the allelochemical juglone, which affects some species greatly while others not at all. The leaf litter and root exudates of some Eucalyptus species are allelopathic for certain soil microbes and plant species. The tree of heaven, Ailanthus altissima, produces allelochemicals in its roots that inhibit the growth of many plants.

I’m familiar with the allelopathic effects of sunflowers (Helianthus) on a great many plants, similarly of dandelions (Taraxacum officinale) — these plants are quadruple-threat invasives, spreading their tiny seeds on the wind, growing very fast, tolerating drought, and suppressing the growth of surrounding plants — and of black walnuts (Juglans nigra), which are especially suppressive of Solanaceae plants (notably, tomatoes), and of species of Eucalyptus.

Now the other pants mentioned above.

Centaurea maculosa. From Wikipedia:

Centaurea maculosa, the spotted knapweed, is a species of Centaurea native to eastern Europe. … Knapweed is a pioneer species found in recently disturbed sites or openings [so it’s ruderal]. Once it has been established at a disturbed site, it continues to spread into the surrounding habitat. This species outcompetes natives through at least three methods: A tap root that sucks up water faster than the root systems of its neighbors; quick spread through high seed production, and low palatability, meaning it is less likely to be chosen as food by herbivores. It is also suspected to be allelopathic, releasing a toxin from its roots that stunts the growth of nearby plants of other species.


This unpleasant plant is very closely related to Centaurea cyanus, the ornamental cornflower, or bachelor’s button:


Alliaria petiolata. From Wikipedia:

Alliaria petiolata is a biennial flowering plant in the Mustard family, Brassicaceae. It is native to Europe, western and central Asia, and northwestern Africa, from Morocco, Iberia and the British Isles, north to northern Scandinavia, and east to northern Pakistan and western China (Xinjiang).

In the first year of growth, plants form clumps of round shaped, slightly wrinkled leaves, that when crushed smell like garlic. The next year plants flower in spring, producing cross shaped white flowers in dense clusters. As the flowering stems bloom they elongate into a spike-like shape. When blooming is complete, plants produce upright fruits that release seeds in mid-summer. Plants are often found growing along the margins of hedges, giving rise to the old British folk name of Jack-by-the-hedge. Other common names include Garlic Mustard, Garlic Root, Hedge Garlic, Sauce-alone, Jack-in-the-bush, Penny Hedge and Poor Man’s Mustard. The genus name Alliaria, “resembling Allium”, refers to the garlic-like odour of the crushed foliage.

… The plant is classified as an invasive species in North America. Since being brought to the United States by settlers [as a culinary herb], it has naturalized and expanded its range to include most of the Northeast and Midwest, as well as southeastern Canada. It is one of the few invasive herbaceous species able to dominate the understory of North American forests and has thus reduced the biodiversity of many areas

… Garlic Mustard produces allelochemicals, mainly in the form of the cyanide compounds allyl isothiocyanate and benzyl isothiocyanate, which suppress mycorrhizal fungi that most plants, including native forest trees, require for optimum growth.


Casuarina/Allocasuarina species. From Wikipedia:

Casuarina is a genus of 17 species in the family Casuarinaceae, native to Australasia, the Indian Subcontinent, southeast Asia, and islands of the western Pacific Ocean [and closely related to species of Allocasuarina].

… They are evergreen shrubs and trees growing to 35 m tall. The foliage consists of slender, much-branched green to grey-green twigs bearing minute scale-leaves in whorls of 5–20. The flowers are produced in small catkin-like inflorescences; the flowers are simple spikes. … The fruit is a woody, oval structure superficially resembling a conifer cone made up of numerous carpels each containing a single seed with a small wing. The generic name is derived from the Malay word for the cassowary, kasuari, alluding to the similarities between the bird’s feathers and the plant’s foliage

… Commonly known as the she-oak, sheoak, ironwood, or beefwood, casuarinas are commonly grown in tropical and subtropical areas throughout the world. The tree has delicate, slender ultimate branches and leaves that are no more than scales, making the tree look more like a wispy conifer.

Casuarina and Allocasuarina spp are strongly suspected of having allelopathic properties, as evidenced by the total or near absence of understory once a mat of litter develops around the plants.

… in the United States it was introduced in the early 1900s, and is now considered an invasive species. The species has nearly quadrupled in southern Florida between 1993 and 2005, where it is known as Australian pine.

C. equisetifolia is widespread in the Hawaiian Islands where it grows both on the seashore in dry, salty, calcareous soils and up in the mountains in high rainfall areas on volcanic soils. It is also an introduced, invasive plant in Bermuda

The tree is not especially protogenic:


Yellow nutsedge. From Wikipedia:

Cyperus esculentus (also called chufa sedge, nut grass, yellow nutsedge, tiger nut sedge, or earth almond) is a crop of the sedge family {Cyperaceae] widespread across much of the world. It is native to most of the Western Hemisphere as well as southern Europe, Africa, Madagascar, the Middle East and the Indian Subcontinent. It has become naturalized in many other regions, including Ukraine, China, Hawaii, Indochina, New Guinea, Java, New South Wales and various oceanic islands.

Cyperus esculentus can be found wild, as a weed, or as a crop. There is evidence for its cultivation in Egypt since the sixth millennium BC, and for several centuries in Southern Europe. In Spain, C. esculentus is cultivated for its edible tubers, called earth almonds or tiger nuts [they are tubers, not nuts], for the preparation of “horchata de chufa”, a sweet, milk-like beverage. However, in most other countries, C. esculentus is considered a weed.

… [It has] a stratified and layered root system, with tubers and roots being interconnected to a depth of 36 cm or more. The tubers are connected by fragile roots that are prone to snapping when pulled, making the root system difficult to remove intact. Intermediate rhizomes can potentially reach a length of 60 cm. The plant can quickly regenerate if a single tuber is left in place. By competing for light, water and nutrients it can reduce the vigour of neighbouring plants.

But that’s not all. From the eXtension website:

Allelopathic substances from yellow nutsedge have reduced growth of corn, soybean, and sweet potato in greenhouse trials


Ailanthus altissima. Now to the tree that literarily grew in Brooklyn and pops up al over the place, even between the sidewalk and walls of buildings here in Palo Alto. From Wikipedia:

Ailanthus altissima … commonly known as tree of heaven [or] ailanthus … The tree grows rapidly and is capable of reaching heights of 15 metres (49 ft) in 25 years. However, the species is also short lived and rarely lives more than 50 years, though its remarkable suckering ability makes it possible for this tree to clone itself indefinitely and live considerably longer (since they are linked to the mother tree and thus partly fed by it, the suckers are less vulnerable than the seedlings and can grow faster).

… In a number of [areas], it has become an invasive species due to its ability both to colonise disturbed areas quickly and to suppress competition with allelopathic chemicals. It is considered a noxious weed in Australia, the United States, New Zealand and many countries of central, eastern and southern Europe. The tree also resprouts vigorously when cut, making its eradication difficult and time consuming.

It also smells foul, and it’s not especially pretty. Despite all that, there was some fashion for planting it as a city street tree, because it’s so very tough. My god, is it tough!


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