(Daisy or Sunflower family)
- Taraxacum japonicum Koidz.
The plant yields lactucopicrin (Kariyone 1971), a sesquiterpene lactone that is potentially allergenic (Mitchell & Dupuis 1971).
- Taraxacum officinale F.H.Wigg.
- (syns Leontodon taraxacum L., Taraxacum dens-leonis Desf., Taraxacum vulgare Schrank)
- Dandelion, Lion's Tooth, Löwenzahn, Dent de Lion, Pissenlit
This species is of almost cosmopolitan distribution, and is often encountered as a troublesome weed. The roasted roots may be used as a coffee substitute, and the leaves are sometimes eaten in salads. A liquid extract from the roots has been used as a bitter and as a mild laxative (Wade 1977). Hartwell (1968) records that the juice of the plant may be applied to treat warts. Wat et al. (1980b) found an extract of the leaves to have phototoxic and weak antibiotic properties against two fungal test micro-organisms.
Ingestion of a decoction of the plant produced itching and tingling erythema, papules, and wheals, followed by desquamation (Smyth 1845).
Contact sensitivity to this species, with cross-sensitivity to Anthemis nobilis L. (see Chamaemelum nobile All.) and Apium graveolens L. (fam. Umbelliferae) was reported by Janke (1950). Three patients with "Australian bush dermatitis" showed positive patch test reactions to the plant; the patients were also contact sensitive to Chrysanthemum L. and Olearia Moench, and, in one of the cases, to other members of the Compositae (Burry et al. 1973). Hausen & Schulz (1978b) and Larrègue et al. (1978) reported allergic contact dermatitis caused by dandelions, and observed cross-sensitivity between dandelion, laurel oil (from Laurus nobilis L., fam. Lauraceae), and liverworts belonging to the genus Frullania Raddi (fam. Jubulaceae). Other patients with contact sensitivity to dandelion were reported by Hausen (1979). Burry (1979) observed a positive patch test reaction to Taraxacum officinale in a patient with "fleabane dermatitis" (see Conyza bonariensis Cronq.). Hausen (1982) identified taraxinic acid-1'-O-β-D-glucoside as an allergen of Taraxacum officinale.
- Tarchonanthus camphoratus L.
The tree has no thorns but a wound from a splinter of its wood produces a troublesome sore, difficult to heal (Watt & Breyer-Brandwijk 1962). The wood has been used for musical instruments (Willis 1973).
- Telekia speciosa Baumg.
- (syn. Buphthalmum speciosum Schreber)
- Large Yellow Ox-Eye
A number of potentially allergenic sesquiterpene lactones have been reported from this species.
- Tessaria integrifolia Ruiz & Pavón
The roots contain α-terthienyl (Chan et al. 1979), a thiophene with phototoxic properties to human skin (see Tagetes L. above).
- Tetradymia DC.
Eight species are found in western North America. The genus is classified in the tribe Heliantheae.
- Tetradymia canescens DC.
- Little Gray Horsebrush, Spineless Gray Horsebrush
- Tetradymia glabrata A.Gray
- Horsebrush, Leaf Horsebrush, Coal Oil Brush
Reported irritant effects of the plants in man (Muenscher 1951, Schwartz et al. 1957) are not well substantiated.
These two North American species cause photodermatitis in sheep upon ingestion (Mathews 1937, Kingsbury 1964). Sheep are usually poisoned in early spring, this being most often observed in Utah and adjacent states in the USA. The sheep develop general debility and photosensitivity leading to a condition known as "big head" — a hyperaemia and swelling of bare patches of skin on the face. Experimental feeding of the plants fails to reproduce the toxic syndrome but it has been found that prior ingestion of black sagebrush (Artemisia nova Nelson) preconditions the sheep for Tetradymia photosensitisation (Johnson 1978).
- Thelesperma megapotamicum Herter
- (syns Thelesperma gracile A.Gray, Cosmidium gracile Nutt., Bidens megapotamica Spreng.)
- False Coreopsis
The fruits have barbed bristles. McCord (1962) listed the plant as being capable of producing dermatitis. Shelmire (1939a) observed no positive patch test reactions to an extract of the plant in 50 patients with "weed dermatitis".
- Thymophylla acerosa Strother
- (syns Dyssodia acerosa DC., Hymenatherum acerosum A.Gray)
Bohlmann et al. (1976) reported the presence of α-terthienyl, a phototoxic thiophene (see Tagetes L.), in the roots of Dyssodia acerosa.
- Thymophylla tenuiloba Small
- (syn. Hymenatherum tenuilobum DC.)
This species has been reported to yield α-terthienyl (Bohlmann & Zdero 1979), a phototoxic thiophene (see Tagetes L.).
- Tripleurospermum maritimum Koch ssp inodorum Appleq.
- (syns Matricaria inodora L., Tripleurospermum inodorum Sch.Bip., Matricaria perforata Mérat)
- Scentless Mayweed
Three farmers developed contact dermatitis from the plant. Patch tests were positive to Matricaria inodora L., negative to German chamomile (Matricaria chamomilla L. var recutita Grierson) (Kocsis 1961).
- Venegasia carpesioides DC.
This species from California, USA and Mexico has been reported to contain eupatoriopicrin (Geissman & Atala 1971), a potentially allergenic sesquiterpene lactone (Mitchell & Dupuis 1971).
The genus is monotypic.
- Verbesina encelioides Benth. & Hook.f.
- (syn. Ximenesia encelioides Cav.)
- Golden Crownbeard
The awned achenes can cause mechanical injury to animals (Hurst 1942). Shelmire (1940) observed contact urticaria from the plant.
This North American species has become locally naturalised in Europe.
- Vernonia anthelmintica Willd.
The fruits are used in the treatment of skin diseases and for repelling moths from woollens (Howes 1974).
Vernodalol, a potentially allergenic elemanolide, has been reported from this species.
- Vernonia baldwini Torr.
- Iron Weed
Cross-sensitivity to this North American species was observed in one of 50 patients with "weed dermatitis" (Shelmire 1939a).
- Vernonia echitifolia Mart.
Bohlmann et al. (1981p) reported small quantities of both sesamin and dehydrozaluzanin C in the roots of this species. The former is known for its role in sesame oil (Sesamum indicum L., fam. Pedaliaceae) dermatitis; the latter is a potentially allergenic guaianolide.