Clarification of the carpel number in Papaverales, Capparales, and Berberidaceae

For more than 170 years there has been a controversy about the organization of the siliqua, a fruit typical for the Brassicaceae and, in modified form s, also for members of Capparaceae, Papaveraceae, and Fumariaceae. Because in the Berberidaceae fruit forms resembling a "semi-siliqua" are produced, they are also controversial. A siliqua is typically furnished with two plac ental regions joined by a septum and dehiscing through detachment of two st erile valves. Modified forms lack a septum and have only one or more than t wo valves, or are indehiscent. The controversial issue is the number of car pels composing a siliqua, typical or modified. Aside from the fact that the nature and phylogeny of the angiosperm organ "carpel" are still insufficie ntly known and therefore speculative, carpel numbers of two, four, and six have been proposed for a bivalvate siliqua; moreover, an "acarpellate" stat e as an axis-derived structure has been postulated. Within the framework of these theories there are additional theories concerning the position, shap e, and fertility or sterility of what are believed to be carpels. Each of t hese concepts is reviewed here, and its morphological basis is checked. Gyn oecial features used as evidence of the manifold hypotheses are shape of th e stigma, zones of dehiscence, structure of the placental regions, vascular pattern, ontogeny, and teratological transformations. They are discussed f or each family and compared in the context of the conclusions derived from them. The result is that Robert Brown's (1817) classical theory, explaining the siliqua as a product of fusion of two transverse carpels with the valv es being opercular structures and the septum formed of placental outgrowths , cannot be invalidated by any of the later theories. Stigmatic lobes shoul d not a priori be equated with carpel tips, and their number is not a defin ite indication of carpel number. The zones of dehiscence are not carpel bor ders but secondary separation tissues within the carpel blade. Massive plac ental regions with complex venation need not be solid carpels. Number and c ourse of vascular bundles may be interpreted in ontogenetic and functional terms, and the concept of vascular conservatism is unsound. Gynoecial growt h centers must not uncritically be equated with carpel primordia. Terata, s uch as tetravalvate siliquae, are not atavisms. Thus, carpel numbers higher than those of placentae in the given gynoecium cannot be ascertained. The gynoecium of Berberidaceae is truly monomerous. The identical organization of the gynoecia in the families concerned demands their explanation by a si ngle theory. Many textbooks, floras, and monographs should be revised from this point of view.