Chrysanthemum Leucanthemum L.

Abstract

Subgenus Leucanthemum (Mill.) Hegi. A perennial herb with oblique, shallow, branched, rhizome and strong adventitious roots. Stems at base prostrate and rooting: otherwise erect, simple or slightly branched (4-) 30-80 (-200) cm furrowed, glabrous to sparsely pubescent. Non-flowering leaf rosettes also produced. Lower leaves on long stalks, spathulate to round, dentate; stem leaves spiral, sessile + amplexicaul, narrow lanceolate or ligulate coarsely toothed often with lobes at the base. Leaves sparsely pubescent and three-nerved. Flower heads mostly solitary on long terminal peduncles, 2 5-5 (-7.5) cm diameter. Involucral bracts narrow with a dark brown scarious sub-marginal area; the outer lanceolate to triangular, the inner more oblong. Receptacle flat. Ray-florets long, 1-2 cm white ligulate, 3-toothed, rarely 0; disk-florets short, 4 mm yellow tubular, with a few glands near the middle of the tube. Palae absent between florets. Heads heterogamous with female ray-florets + abortive stamens and hermaphrodite disk-florets; rarely homogamous with all florets hermaphrodite. Fruits are achenes lacking a pappus, obovoid to cylindrical, 2-3 x 0 8-1 mm for both disk and ray, grey-silvery with (5-) 6 (-10)? equal ribs, grooves dark coloured. Achenes crowned by remains of stigmata. Ray achenes with a border absent in disk achenes. Weight of 1000 achenes variable: 038+0-16 g for both disk and ray. A variable species. Hegi describes five subspecies in central Europe, but many variants have been named, e.g. Cavillier in Burnat (1916), Horvatic (1935). The polymorphy is most striking when material from the whole range of the species is considered. Diploid and tetraploid races of C. keucanthemum s. lat. may be regarded as two species, C. keucanthemum s. str. and C. ircutianum Turcz. s. lat., although Bocher & Larsen (1957) point out that there are some varieties of one race which approach the other. The distinguishing features of the two groups are shown in Table 1. Most British forms belong to ssp. keucanthemum L. (ssp. triviale Gaud.), and are the diploid race. Ciapham in Clapham, Tutin & Warburg (1962) does not divide the species.