Fruit structure and systematics of Monimiaceae s.s. (Laurales)

Fruit structure ( anatomy) was studied in 27 species of 15 genera of Monimiaceae s.s. Almost all have apocarpous gynoecia, with the carpels more or less surrounded by a floral cup. The fruitlets are presented on the opened floral cup, which, depending on its pre- and post-floral development, differentially contributes to the attractive part of the mature fruit. Morphologically similar fruits may differ conspicuously in anatomical structure. Based on anatomical characters two different fruit forms were found: drupe(let)s ( with compact sclerenchymatic endocarp forming a stone: putamen) and berry( let) s ( with parenchymatic endocarp, and mesocarp parenchyma containing isolated sclereid nests). Four types of drupelets differing by the endocarp structure were tentatively distinguished: (1) the Monimia-type has a many-cell-layered putamen of large isodiametric sclereids, interrupted on the ventral side by few radial rows of small sclereids; (2) the Hortonia-type has a few-cell-layered putamen of isodiametric, especially thick-walled sclereids - it may be composed of two lateral halves, i.e. with the sclerenchyma partially interrupted on the ventral and dorsal sides ( but without rows of small sclereids); ( 3) the Mollinedia-type has a few-cell-layered putamen, with more or less radially elongate sclereids with wavy cell walls; and (4) the Hedycarya-type has a one-cell-layered putamen of pronouncedly radially elongate sclereids with wavy cell walls. Drupelets of some taxa with a single-cell-layered endocarp with only weakly thickened cell walls may represent a transition from drupelets to berrylets. The fruit structure supports three major clades recognized earlier by morphological studies and by molecular phylogenetic analyses: (1) Monimioideae (Monimia-type drupelets), (2) Hortonieae of Mollinedioideae (Hortonia-type drupelets), and ( 3) the remainder of Mollinedioideae (Hedycarya- and Mollinedia-types) and berrylets. Fruit structure also supports the close relationship of Monimiaceae and Lauraceae. (c) 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007.