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Taraxacum Linn.

蒲公英属

Description from Flora of China

Herbs, rosulate, perennial, with a taproot, root head sometimes with a tunic (covered with dry brown remnants of petioles from previous years). Stems 1 to sometimes several, hollow, leafless (scape), unbranched, rarely with 1-3 branches. Plant indumentum consisting of arachnoid hairs; leaf and scape hairs sometimes on low protuberances or ridges; hairs on floret tube often straight and simple. Leaves entire or variously lobed, runcinate to pinnatisect. Capitulum pointing upward or downward after anthesis. Involucre with two distinct series of phyllaries. Some of phyllaries often corniculate or horned at apex; outer phyllaries variable in length and shape (imbricate) or almost uniform (not imbricate), usually substantially shorter than inner ones, appressed to reflexed, glabrous to ciliate or with arachnoid surfaces, unbordered to variously pale to whitish bordered. Receptacle naked, glabrous or sparsely arachnoid. Florets yellow, white, whitish yellow, pale or deep pink, orange, brownish orange, or reddish brown; ligules flat, involute, or tubular, adaxial epidermal cell cuticle ± domed and transversely striate. Achene whitish, straw-brown, ochraceous, reddish, reddish brown, deep brown, or ± black, usually composed of a body, which includes a narrowed but equally colored cone, and apically with a beak but cone sometimes indistinct or not developed; body spinulose and/or squamulose in upper part (below cone), often tuberculate below or completely or almost smooth, or spinulose and tuberculate throughout, abruptly or gradually narrowing into cone (when cone developed); beak usually longer than achene body including cone or short, sometimes not developed at all, thin or thick. Pappus with numerous scabrid bristles, white, yellowish, or light reddish brown. Plants with agamospermous reproduction or sexual, self-incompatible or rarely self-compatible. Chromosome base number x = 8 (diploids to dodecaploids). Diploids always sexual, tetraploids usually agamospermous [three tetraploid sexual species known in Taraxacum sect. Piesis], other polyploids agamospermous.

The genus Taraxacum represents a taxonomic complexity in the whole of its range and in China in particular. Basic features of dandelions relevant for the taxonomy at the species level are: 1) There is a low level of structural morphological differentiation. 2) There is a coexistence of agamospermy and sexuality. 3) There is complex hybridity. 4) There is extensive polyploidy. 5) There is a large number of taxa. Thus, any taxonomic study of this genus should follow a few principles: 1) A great attention should be paid to the reproduction in population structures because different modes of reproduction usually mean very different variation ranges, and species in Taraxacum differ substantially in this respect. 2) The taxonomic study must be started at the lowest level of recognizable units in order to avoid a loss of information, and later lumping should be a result of a knowledge of the population structure of all subordinate units. 3) The category of section is equally important as that of species in Taraxacum. Because of very different reproduction systems, the species have incommensurable variation ranges, and, for a non-specialist in particular, the most useful traditional rank covering both sexual and agamospermous taxa is that of section. Moreover, in an imperfectly explored region, there might be sections in which the species remain unknown or undescribed because of the insufficient material, although the very occurrence of the given section in the territory studied is unquestionable. The latter case requires using sections as one of the basic categories in taxonomic hierarchy.

Notes on descriptions: Achenes are measured to include the cone, a narrow part of the achene connecting achene body with the beak. Middle leaves are those well developed during full anthesis; outer leaves are the first spring leaves and are usually less deeply lobed or not divided. Inner leaves develop at the end of anthesis and are usually more deeply divided than the others. In the descriptions, middle leaves are taxonomically the most important. Outer phyllaries are described as imbricate when the outermost ones of them are broader and shorter than the successive more inner ones (often the outermost ones are ovate to ovate-lanceolate and the others lanceolate to narrowly lanceolate; the distal parts of the latter are clearly visible above the outermost ones). In species with imbricate outer phyllaries, the bracket measurements usually refer to the innermost outer phyllaries (the longest and the narrowest ones).

In several Chinese Taraxacum sections achene color substantially changes before maturity. Particularly in T. sect. Tibetana and T. sect. Emodensia, two color series can be recognized: in one series achenes are pale reddish ochraceous or ochraceous when immature and become darker red to reach deep reddish castaneous brown or deep red when mature, and the other series starts with pale grayish or straw-colored achenes, becoming gray and reaching almost black at full maturity.

Variation is also observed in the development of a horn on the outer phyllaries. The first capitula to blossom often have flat or callose outer and/or inner phyllaries while later capitula have a distinct horn near the apex of the phyllaries. This characteristic mainly concerns Taraxacum sect. Borealia, T. sect. Emodensia, and T. sect. Mongolica.

The references to Higher Pl. China in the following treatment of Taraxacum refers to the treatment of Taraxacum by X. J. Ge (11: 766-786. 2005).

More than 2,500 species: mainly in the Arctic and temperate zones of the N Hemisphere with main diversity in mountains of Eurasia, a few species in temperate regions of the S Hemisphere; 116 species (81 endemic, three introduced) in China.

(Authors: Ge Xuejun (葛学军); Jan Kirschner, Jan ěp嫕ek)


 

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