Aristolochia fimbriata (Aristolochiaceae: Piperales) exhibits highly synorganized flowers with a single convoluted structure forming a petaloid perianth that surrounds the gynostemium, putatively formed by the congenital fusion between stamens and the upper portion of the carpels. Here we present the flower development and morphology of A. fimbriata, together with the expression of the key regulatory genes that participate in flower development, particularly those likely controlling perianth identity. A. fimbriata is a member of the magnoliids, and thus gene expression detected for all ABCE MADS-box genes in this taxon, can also help to elucidate patterns of gene expression prior the independent duplications of these genes in eudicots and monocots. Using both floral development and anatomy in combination with the isolation of MADS-box gene homologs, gene phylogenetic analyses and expression studies (both by reverse transcription PCR and in situ hybridization), we present hypotheses on floral organ identity genes involved in the formation of this bizarre flower. We found that most MADS-box genes were expressed in vegetative and reproductive tissues with the exception of AfimSEP2, AfimAGL6, and AfimSTK transcripts that are only found in flowers and capsules but are not detected in leaves. Two genes show ubiquitous expression; AfimFUL that is found in all floral organs at all developmental stages as well as in leaves and capsules, and AfimAG that has low expression in leaves and is found in all floral organs at all stages with a considerable reduction of expression in the limb of anthetic flowers. Our results indicate that expression of AfimFUL is indicative of pleiotropic roles and not of a perianth identity specific function. On the other hand, expression of B-class genes, AfimAP3 and AfimPI, suggests their conserved role in stamen identity and corroborates that the perianth is sepal and not petal-derived. Our data also postulates an AGL6 ortholog as a candidate gene for sepal identity in the Aristolochiaceae and provides testable hypothesis for a modified ABCE model in synorganized magnoliid flowers.

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In parasitic plants, the reduction in plastid genome (plastome) size and content is driven predominantly by the loss of photosynthetic genes. The first completed mitochondrial genomes (mitogenomes) from parasitic mistletoes also exhibit significant degradation, but the generality of this observation for other parasitic plants is unclear. We sequenced the complete mitogenome and plastome of the hemiparasite Castilleja paramensis (Orobanchaceae) and compared them with additional holoparasitic, hemiparasitic and nonparasitic species from Orobanchaceae. Comparative mitogenomic analysis revealed minimal gene loss among the seven Orobanchaceae species, indicating the retention of typical mitochondrial function among Orobanchaceae species. Phylogenetic analysis demonstrated that the mobile cox1 intron was acquired vertically from a nonparasitic ancestor, arguing against a role for Orobanchaceae parasites in the horizontal acquisition or distribution of this intron. The C. paramensis plastome has retained nearly all genes except for the recent pseudogenization of four subunits of the NAD(P)H dehydrogenase complex, indicating a very early stage of plastome degradation. These results lend support to the notion that loss of ndh gene function is the first step of plastome degradation in the transition to a parasitic lifestyle.

Inflorescence and floral morphology and development were investigated in Aragoa (Plantaginaceae) and related genera. Each inflorescence of Aragoa is a reduced, axillary raceme, on which the actinomorphic floral apices generally arise successively. The inflorescences of Aragoa and Plantago are polytelic and lateral. The five sepals emerge from the abaxial to the adaxial side of the floral apex, but at maturity, the calyx is actinomorphic. The four stamens arise simultaneously and before emergence of the petals. The four petals emerge unidirectionally united, but the corolla becomes actinomorphic. Aestivation is cochlear ascendent. The two united carpels initiate simultaneously. The abaxial-adaxial inception of the calyx and corolla during early floral development in genera such as Aragoa, Digitalis, Plantago, and Veronica may indicate that the zygomorphic condition is ancestral in those genera. The tetramerous corolla, which is actinomorphic during middle and late development, and the presence of four stamens are possible synapomophies of the clade (Aragoa þ Plantago). Pentamery of the calyx and corolla appears to be plesiomorphic in the broader AragoaAngelonia clade. Characters related to development and morphology of inflorescences and flowers of Aragoa are essentially similar to those found in Plantago, which is consistent with the molecular-based sister group relationship between these genera.

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A study of inflorescence and flower development in 12 species from four of the six subgenera of Gunnera (Gunneraceae) was carried out. In the species of subgenus Panke, initiation of floral apices along the partial inflorescences is acropetal but ends up in the late formation of a terminal flower, forming a cyme at maturity. The terminal flower is the largest and the most complete in terms of merosity and number of whorls and thus it is the most diagnostic in terms of species-level taxonomy. The lateral flowers undergo a basipetal gradient of organ reduction along the inflorescence, ranging from bisexual flowers (towards the distal region) to functionally (i.e. with staminodia) and structurally female flowers (towards the proximal region). Our results show that the terminal structure in Gunnera is a flower rather than a pseudanthium. The terminal flower is disymmetric, dimerous and bisexual, representing the common bauplan for Gunnera flowers. It has a differentiated perianth with two sepals and two alternate petals, the latter opposite the stamens and carpels. Comparisons with other members of the core eudicots with labile floral construction are addressed. We propose vegetative and floral putative synapomorphies for the sister-group relationship between Gunneraceae and Myrothamnaceae.