Embryological studies indicate Eupatorium laevigatum to have Antennaria type diplospory with precocious embryony. The embryo sac is of the Polygonum type and the polar nuclei fuse before anthesis (maturation of the stamens). Endosperm development is autonomous and the central cell divides only after the initial stages of embryo formation. It is estimated that about 10% of the florets in anthesis contain an undivided egg which can be used for sexual reproduction. The study of microsporogenesis

more »

... vealed abnormalities in chromosome pairing which result in the formation of univalents, bivalents, trivalents and higher polyvalents, with the consequent production of lagging chromosomes, unbalanced nuclei, micronuclei and sterile pollen. We found that, as represented by the material studied, E. laevigatum is an autohexaploid (2n = 6x = 60) in which each chromosome of a basic set of ten chromosomes is repeated six times and that E. laevigatum is an essentialy obligate apomictic. Figure 2 -Embryo sac and embryo formation in Eupatorium laevigatum. Key: a = Embryo sac showing egg and two polar nuclei (PN); b = Embryo sac with egg and central cell (CC); c = Embryo sac with embryo (EMB) and central cell (CC); d = Embryo sac with initial divisions of embryo (EMB) and endosperm (END). All 540x.