Argemone × hybrida is described as a natural hybrid of A. mexicana and A. ochroleuca, based on a collection from La Palma (Canary Islands, Spain), where both parents are found growing in close proximity. This hybrid may be more widespread but overlooked. Distinguishing features of all three taxa are thoroughly discussed and illustrated.
Evolutionary relationships withinArgemone (Papaveraceae) were inferred from nucleotide variation in nuclear ribosomal DNA. A complete representation of the genus was achieved by using herbarium material to a large extent (74%). Four distinct clades can be recognized based on the molecular results. The support for the different clades varies greatly due to a very uneven distribution of characters. Although some clades are largely unresolved, some unexpected relationships, for example the sister group relationship of the relict speciesA. subintegrifolia to the rest ofArgemone, were found. The evolution of morphological and alkaloid characters against the background of the obtained phylogeny is discussed. Whereas the morphological characters provide some support for the phylogeny found, the alkaloid characters turned out not to contain much phylogenetic information. Past difficulties in recognizing phylogenetic relationships withinArgemone result from largely continuous morphological variation and from parallelisms correlated with and probably caused by polyploidization.
A new species ofArgemone (Papaveraceae),A. subalpina, is recognized from the subalpine glades of Sierra Peña Nevada, Nuevo León, México. It is the first member of the poppy family
to be associated with timberline vegetation in the New World. The new taxon is closely related toA. platyceras of the Mexican transvolcanic belt, but differs by retrorse cauline spines, broadly ellipsoid flower buds to 20 mm long, caudate
sepal norns 3–5 mm long, and recurved fruit spines.
Cytogenetic investigations of 5 diploid Argemone species and their hybrids were undertaken. Correlative informations on the morphology, cytology, crossability and interfertility have been secured to understand the mechanism crossability and interfertility have been secured to understand the mechanism of speciation in the genus.
All species studied possess 14 bivalents, normal meiosis and perfect pollen and seed fertility.
Statistical comparisons regarding two meiotic metrics (frequency of ring bivalents; chiasma frequency) between some of the species revealed significant differences.
Crosses were attempted in all species combinations, and hybrids were obtained in several. On the basis of pollen and seed fertility these were classified as fortile (mexicana × subfusiformis; subjusiformis × mexicana f. leiocarpa) and semifertile (mexicana × albiflora; subjusiformis × platyceras; mexicana f. leiocarpa × platyceras) hybrids. F1's are intermediate, qualitatively they exhibit heterosis.
Meiosis was analysed in all hybrids (pachynema; M-I, A-I) and several metrics e.g. ring bivalent frequency, chiasma frequency were taken as indices of genome affinity.
It is suggested that mexicana, mexicana f. leiocarpa and subfusiformis are taxonomically close and display only allelic differentiation: albiflora and platyceras are structurally distinct from each other. Several structural changes e.g. duplications, inversions, translocations etc. were involved in their differentiation.
The role of isolation barriers in maintaining species differentiation is discussed.