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A floral developmental series was determined for Persea americana (Lauraceae, avocado), and the floral morphology of this species was compared with available data for other members of Persea. We compared the structure of the inflorescence and flower with that of vegetative shoots with respect to phyllotaxy and leaf shape. The inflorescence is a determinate thyrse (panicle) with variable numbers of lateral branches. Staminal glands in Persea may represent abaxial-marginal emergences rather than stamens. However, these glands are occasionally involved in transitions to pollen sacs and ovary margins. Stigmas, pollen sacs, staminal appendages, glands of staminodes, and margins of tepals share features that are subjectively associated with ‘androecia.’ In the innermost androecial whorl, staminodial glands appear united because of the reduction of the middle portion to a staminodial apex. The apex of staminodes is homologous to the filament and anther, as well as to the stigma of the carpel, and corresponds to the connective tip in other basal angiosperms. In Persea, the connective and the staminode apex also correspond to the body of the tepal (i.e., all but the margin). Above a constriction (stipe), the carpel forms a cross zone bearing the single ovule; this cross zone also corresponds to the thecae in stamens, similar to observations for other basal angiosperms. [ABSTRACT FROM AUTHOR]

The perianth of Persea americana (Lauraceae) consists of two whorls of morphologically similar laminar organs, termed tepals. Closely related Persea borbonia, however, produces a dimorphic perianth with smaller outer tepals. To assess whether homologues of floral organ identity genes in Persea may play a role in shaping this dimorphic perianth, we compared their expression patterns in the two species. A homologue of AP1 (A-function) is expressed at low levels in both perianth types but was not tepal specific. Homologues of AGL6, however, show the tepal-specific expression pattern expected of A-function genes. Homologues of AP3 and PI (B-function) are expressed in tepals of both perianth types, indicating that perianth dimorphism in Persea is not regulated by these genes. Differential expression across the dimorphic perianth as absence late in outer tepal development was evident for homologues of AG (C-function) and SEP3 (E-function). Genetic studies in model systems indicate a conserved role for AG homologues in specifying stamen and carpel identity, but the expression pattern in Persea indicates a novel role in perianth development. On the basis of gene expression and the occasional presence of tepaloid organs in stamen whorls, we hypothesize that the tepals of Persea and perhaps other Lauraceae are derived from stamens. [ABSTRACT FROM AUTHOR]