Diversity and lability of floral phyllotaxis in the pluricarpellate families of core Laurales (Gomortegaceae, Atherospermataceae, Siparunaceae, Monimiaceae)

Abstract

Floral phyllotaxis of Laurales (Magnoliidae) is poorly and sometimes conflictingly documented, especially in the pluricarpellate families of the core Laurales (Gomortegaceae, Atherospermataceae, Siparunaceae, Monimiaceae). In this study four types of floral phyllotaxis were recovered: Fibonacci spiral, simple-whorled (decussate), complex-whorled, and irregular. Whorled and spiral phyllotaxis co‐occur in all families except Gomortegaceae and even vary within a species in some Mollinedioideae (Monimiaceae). Complex‐whorled floral phyllotaxis with two or more organs in a position where only one is expected and changes in merism are especially prominent in Atherospermataceae and Monimiaceae. The most elaborate complex‐whorled phyllotaxis pattern (leading to 8‐merous whorls) is present in flowers with a flat floral base. Presence of a hyperstigma is correlated with double positions in the perianth. Flowers with low organ number commonly have simple‐whorled phyllotaxis; flowers with high organ number have complex‐whorled or irregular patterns. Spiral phyllotaxis occurs in flowers with a broad range of organ numbers. Irregularities in organ sequence were found at the periphery of the gynoecium in some Atherospermataceae and Monimiaceae, involving staminodes, carpellodes, and carpels. In Laurales, floral phyllotaxis diversity appears to have evolved from spiral phyllotaxis, independently in Atherospermataceae, Siparunaceae, and Monimiaceae.