spore ontogeny (noun, ascospore term,spore morphology term, pl. spore ontogenies) – the development of the ascospore. In ascospores with distinct pigmentation, wall differentiation and ornamentation up to four stages may be distinguished: (1) immature: not pigmented, often without septa or with a thin, barely visible septum, sometimes with apically wall thickenings but otherwise with no distinct structures, no ornamentation; (2) premature: faintly pigmented, septa often thin, but sometimes beginning to thicken, other wall thickenings sometimes present, becoming reduced or remaining persistent, ornamentation barely visible; (3) mature: pigmentation obvious, septum and wall structures distinct, ornamentation well developed; (4) overmature. pigmentation darkening, spore structures like ornamentation often becoming more pronounced but sometimes disintegrating, wall thickenings frequently becoming reduced again. In ascospores that form septa two ontogenies have been described: A-ontogeny: early septum formation; spore septa form in immature spores even before other structures like apically thickenings become visible or before the spore becomes pigmented. B-ontogeny: late septum formation; spore septa form in premature or mature spores, i. e., after apical thickenings become visible or after the spore becomes pigmented.