The morphological variation and systematic value of stamen pairs in the Magnoliatae

Abstract

The distribution of paired stamens has been investigated in the Magnoliatae. Stamens can be inserted in pairs as the result of two developmental processes: (a) spatial shifts in the flower caused by the transition of a spiral into a cyclic arrangement of floral parts or (b) dédoublement of complex primordia. The first case is linked with a progressive loss of stamen whorls, ultimately leading to the replacement of all pairs by single stamens. Outer paired stamens are characteristic for polycyclic androecia and are often retained when the upper stamen whorls vanish. The outer pairs may be replaced by petals in some cases or by single stamens in other. The second situation arises by the splitting of complex primordia in two secondary primordia or by the independent initiation of the stamens of a pair. Replacement of single stamens by pairs reflects an increase in the pollination potential and has arisen several times, mainly in relation with oligomerous androecia. The distribution of these two types of stamen pairs on a Dahlgrenogram confirms the existence of two groups. These groups correspond more or less with the presence of the characters polymery and oligomery, proposed by RONSE DECRAENE & SMETS (1987, 1993b, 1995b).

Towards an ontogenetic understanding of inflorescence diversity

“…They are usually easy to distinguish by their one-flowered vs. several-flowered presentation. However, considering FM expansion (Ronse de Craene and Smets, 1991), dédoublement (Ronse de Craene and Smets, 1996) and fascicle formation (Rudall, 2008) on the flower side, and extreme flower reduction (Prenner and Rudall, 2007), fasciation (Sokoloff et al, 2007) and abnormal terminal structures (Rudall and Bateman, 2003;Sokoloff et al, 2006) on the FU side, it may be difficult to clearly recognize the boundary between flowers and FUs.…”

Interaction between Floral Merism and Symmetry: Evidence from Fasciated Mutant of Lupinus angustifolius L. (Leguminosae)

“…More often, a number of sites prepatterned for stamens remains the same (i.e., five per whorl) but every site may initiate two or three stamens instead of one. It is the so-called splitting or dédoublement of stamens (Figure 2K-L and Figure 3F), which is not unique among angiosperms [22] and may occur either sporadically or as a component of normal floral development. The situation in Lupinus flowers seems identical with patterning of leaves on a fasciated meristem, when pairs of leaves emerge instead of one (Figure 1J), i.e., a blastozone of corolla and androecium becomes enlarged and splits into two or more organ primordia.…”