International audience ; The advent of reproduction by seeds was one of the most essential evolutionary steps in plant history: the vast majority of living plants are seed plants (spermatophytes). The seed habit includes the following set of defining characteristics: (1) heterospory, (2) occurrence of a single megaspore that germinates within an indehiscent megasporangium (nucellus) retained on the sporophyte, (3) enclosure of the megasporangium in an integument, and (4) capture of pollen before seed dispersal (Rothwell & Scheckler, 1988; Haig & Westoby, 1989). Contrasting hypotheses about the single / multiple, saltational / gradual origin of the seed habit (Chaloner, 1989; Galtier & Rowe, 1989; DiMichele et alii, 1989; Bateman & DiMichele, 1994), and identification of the closest relatives of seed plants (aneurophytalean or archaeopteridalean progymnosperms) (Rothwell & Erwin, 1987; Rothwell & Serbet, 1994; Marshall & Hemsley, 2003) are still matters of considerable debate. Early seeds did not possess the whole set of characters that define modern seeds. They lacked a true micropyle and an entire integument, and none has yet been discovered containing an embryo. Hence they are called preovules. A suite of characters observed in the Late Devonian preovules Moresnetia and Elkinsia and in a number of younger taxa define hydrasperman reproduction (Rothwell & Scheckler, 1988). In hydrasperman preovules, prepollen capture was realized by the modified apex of the nucellus. Prepollen were directed into a hollow lagenostome, then retained in a pollen chamber. A central column attached to the pollen chamber floor sealed the chamber to provide optimal conditions for prepollen germination. The hydrasperman syndrome has been presented as shared by all basal members of the seed plant clade (Rothwell & Scheckler, 1988). Discovery of the Lower Carboniferous preovule Coumiasperma challenged this view. Galtier and Rowe (1989, 1991) suggested that the possession of a massive nucellar tip and ...