Floral ontogeny of Knema and Horsfieldia (Myristicaceae): evidence for a complex androecial evolution

Abstract

The floral ontogeny of two species of Knema and one of Horsfieldia was examined and described using scanning electron microscopy. The perianth is trimerous with three tepals arising in succession. Pistillate flowers have a rounded floral apex with a convex top. The single carpel primordium is initiated along the margin of the bud and develops a plicate shape with an apical bilobed stigma. In staminate flowers, the floral apex is broadly hemispherical with a somewhat three‐sided shape. Several anther primordia are initiated almost simultaneously around the margin of the floral apex. In Horsfieldia, stamens extend laterally in antetepalous groups, whereas, in Knema, anthers form two whorls. The alternitepalous stamens were found to be different from the antetepalous stamens, which are pressed within a limited space. The anther primordia remain adnate to the receptacle and grow longitudinally, producing a pair of microsporangia. The central area of the floral apex persists as an undifferentiated residuum without any trace of a gynoecium. Myristicaceous anthers are basically homologous, although the number of anthers, pollen sacs and shape of the androecium are variable. The evolution of the androecium is discussed in the family, with opposing possibilities for reductions and increases in anther number in Myristicaceae. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164, 42–52.

Origin and evolution of petals in angiosperms

“…Magnoliaceae, Annonaceae) is in many ways comparable to the bipartite perianth of core eudicots, although it certainly has a separate origin. In Myristicaceae, as in Aristolochiaceae and Lactoridaceae, the perianth is reduced to a single whorl with clear sepaloid characteristics , Xu & Ronse De Craene 2010. The ancestral number of perianth whorls for the magnoliids is reconstructed as more than two by Endress & Doyle (2009), with a repetitive derivation of a single or two whorls of perianth parts.…”

“…(2) In the absence of the C-class MADS-box gene AGAMOUS (AG) or its orthologs, activity of B-class MADS-box genes is necessary for development of the petal in the second whorl of the flower (Jack et al 1992, Mizukami & Ma 1992, Bradley et al 1993, Goto & Meyerowitz 1994. (3) Persistent activity of B-class MADS-box genes through late stages of petal development is necessary to maintain the expression of characteristic petal features (Bowman et al 1991, Sommer et al 1991, Zachgo et al 1995. (4) Heterotopic expression of Bclass MADS-box genes in the first-whorl sepals of the flower is sufficient to induce ectopic petal morphology (Coen & Meyer owitz 1991, Krizek & Meyerowitz 1996.…”

The end of the year - looking backwards and looking forwards

“…Morphological investigations (e.g. Carlquist, ; Davies & Stpiczyńska, ; García‐Verdugo et al ., ; Pimentel, Catalán & Sahuquillo, ; Pole, ; Xu & Ronse De Craene, ; Zhang & Ren, ; Zhao et al ., ), including morphometric studies (e.g. Pedersen, ), alone or in combination with genetic data, can be used to improve understanding of evolutionary patterns and clarify patterns of relationships among taxa, and articles of this type feature frequently in the journal.…”

Modern plant morphological studies

“…It is therefore not surprising that flowers and their organs as well as their functional properties have been the focus of countless studies ranging from ontogenetic (e.g. Ren, Chang & Endress, ; Xu & Ronse De Craene, ; Zhang & Ren, ; Zhao et al ., ) to comparative‐systematic (e.g. Matthews & Endress, ; van der Niet, Liltved & Johnson, ) and studies on different aspects of pollination biology (e.g.…”