| Garhadiolus papposus Boiss. et Buhse is one of the very common ephemeral Asteraceae species that germinates in early spring in the Junggar Desert. It produces three types of achenes (peripheral, intermediate, and central) that differ in morphology,dispersal or germination behavior in one head. In this paper, the morphological, dispersal, germination and dormancy characteristics of the there morphs were observed and analyzed both in field and indoors, and the ecological adaptive strategy of the species was discussed. The main results are as follows:(1)The three types of achenes differ significantly in the number, shape, color, mass, length and density of pappus and embryo size. Peripheral achenes, which are subtended by the inner involucral bracts (phyllaries), are smooth, 118.10±1.30mg (means±SE) per 100 achenes, columnar and arcuate, yellow or yellow whitish, 6.67±0.10mm in length and have a scarcely-developed pappus. Central achenes with numerous conspicuous longitudinal thin ribs are 69.00±0.60mg per 100 achenes, columnar and arcuate or straight, brown, elongated (with a length of 9.74±0.14mm), and have a well developed pappus. Intermediate achenes represent a range of morphologies between the"pure"central and peripheral types. In one head, the central and intermediate achenes are more numerous than peripheral ones (5.77±0.13 vs 5.39±0.14 vs 5.24±0.05). In addition, central and intermediate achenes have a thinner and anatomically different pericarp (half as much biomass) compared to peripheral achenes (69.7μm vs 82.1μm vs 156.7μm), and embryos in peripheral achenes are heavier than those in central and intermediate achenes (46.70±0.50mg vs 36.80±0.30mg vs 36.90±0.30mg per 100 embryos).(2)The three morphs differ in dispersal. In the laboratory, dispersal distance was greater for central than for intermediate achenes and greater for intermediate than peripheral achenes. In the field, central achenes can easily be dispersed a long distance by wind, whereas peripheral achenes, which are covered by lignified phyllaries, remain on the capitulum after maturation and are dispersed, close to the mother plants, only when the capitulum breaks apart. Dispersal features of intermediate achenes lie midway between those of central and peripheral achenes.(3)The three morphs differ in germination requirements. Fresh central achenes germinated to 10-21% in light at 15/2℃and 20/10℃, while intermediate and peripheral achenes germinated to <5%. Germination was enhanced by excising the embryo in peripheral but not in intermediate achenes. For peripheral and intermediate achenes, pericarps and/or phyllaries did not inhibit germination of isolated embryos, indicating that water-soluble germination inhibitors are not present in these structures. For central and intermediate achenes, germination percentage increased with duration of dry storage at room temperature (afterripening). Darkness decreased germination of central and intermediate achenes, while peripheral ones did not germinate in any condition. These differences in germination may be caused by low growth potential of the embryo and mechanical resistance (to embryo growth) of the thick pericarp and/or lignified phyllaries.The morphological,dispersal,dormancy and germination characteristics of the three kinds of achenes in G. papposus have significant ecological consequences in distribution of achenes to new areas, development of seedlings, population persistence and expansion and competition among offspring. Heterocarpy may be partly responsible for the success of G. papposus in the Junggar desert.
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