Bilocular

A phylogenetic trend between two forms of gynoecia within Apiales may be of interest. In spite of the lack of morphological limitations (Weberling 1989; Erbar and Leins 1996, 2004; Leins and Erbar 2004), it is uncertain if the state found in Pittosporaceae is ancestral within Apiales. Stevens (2009) proposes that Pittosporaceae floral form is derived rather than plesiomorphic, from which Apiaceae + Araliaceae originated. Understanding gynoecia evolution in Apiales is challenged by unresolved relationships between Pittosporaceae and other monophyletic families within Apiales. However, several evolutionary studies find Pittosporaceae nested within the Araliaceae–Apiaceae alliance (Andersson, 2006; Nicolas et al., 2009). (Plunkett et al., 1996; Chandler and Plunkett, 2004).

In this perspective, the Araliaceae genus Seemannaralia, which has a gynoecium similar to Pittosporaceae, may help understand the evolution of floral traits in Apiales. This South African monospecific genus has a unilocular gynoecium with apically attached ovules, according to reports (Burtt and Dickison, 1975). As Seemannaralia’s location within Araliaceae is firmly verified by molecular investigations and direct links to Pittosporaceae are doubtful (Wen et al., 2001; Plunkett et al., 2004a; Lowry et al., 2004), its gynoecium should be regarded as derived from the state typical of most Apiales taxa. Seemannaralia may demonstrate parallelism in the metamorphosis of Apiales gynoecia. Seemannaralia is a little known genus, and its flowers and fruits were studied to answer issues about gynoecium evolution in Apiales.

Small to medium-sized Seemannaralia gerrardii has lobed leaves. This species is found in KwaZulu-Natal and Mpumalanga in eastern South Africa (Burtt and Dickison, 1975). Seemann (1866) named the species Cussonia gerrardii, but Viguier (1906) separated it as Seemannaralia R.Vig. Cussonia is another African Araliaceae genus. Although Seemannaralia differs from Cussonia by its imbricate petal aestivation and dry laterally compressed fruit, a tight link between these species was recently substantiated by molecular data (Plunkett et al., 2004b). The placement of Seemannaralia within other Araliaceae groupings suggested by Viguier (1906) and Hutchinson (1967) is not supported by molecular data (Wen et al., 2001; Plunkett et al., 2004b; Lowry et al., 2004) or comprehensive morphological analyses (Burtt and Dickison, 1975).

By observing that the blooms had a unilocular ovary formed by two fused carpels (a paracarpous gynoecium), Burtt and Dickison (1975) underscored Seemannaralia’s unique taxonomic status. According to Burtt and Dickison (1975), Seemannaralia’s gynoecium lacks a synascidiate zone or has a very small one. Since the ovule attachment in Seemannaralia is apical, they must be affixed to the symplicate zone. As indicated above, this extraordinary floral trait is not documented elsewhere in Araliaceae, whose most of members have di- to pentamerous syncarpous gynoecia with separate ovarian locules (Philipson, 1970; Eyde and Tseng, 1971; Nuraliev et al., 2010). All Cussonia species have a dimerous gynoecium. One-seeded fruits of Cussonia natalensis (Strey, 1981) are created from bilocular ovaries (Sonder, 1862; Reyneke, 1981), and their fertile and sterile locule septa remain intact (A. A. Oskolski, pers. obs.).

Unilocular ovaries are seen in Arthrophyllum, Osmoxylon micranthum, and Cuphocarpus. Unilocular ovaries of Arthrophyllum and Osmoxylon are generated by single carpels and have a well-developed ascidiate zone (Baumann-Bodenheim, 1955; Philipson, 1970, 1979). So, these species may not differ from other Araliaceae in ascidiate and plicate zone length. The evolutionary location of taxa with monocarpellate unilocular ovaries (Wen, 2001; Plunkett et al., 2004b) shows that the unilocular ovary is derived from bi- or multilocular ovaries in Araliaceae through a reduction in carpels.

Seemannaralia differs from other Araliaceae in the presence of a well-developed symplicate zone, with the synascidiate zone either nonexistent or extremely short, and in ovule insertion in the symplicate zone (rather than in the cross-zone). The current study reexamines Seemannaralia’s floral structure with a focus on its gynoecium. This is part of a larger study on meristic floral morphology in Araliaceae (Sokoloff et al., 2007; Nuraliev et al., 2009, 2010).

Products and Methods

Inflorescences of Seemannaralia gerrardii (Seem.) R.Vig. were gathered by the first and third authors and B. J. de Villiers in April 2007 in KwaZulu-Natal, South Africa (B.J. de Villiers 97 and 107; voucher specimens placed in JRAU). Flowers and fruits were treated in FAA (5% formalin, 5% acetic acid, 90% ethyl alcohol) and stored in 70% ethanol. For light microscopy, sections were 15–25 m thick using paraffin embedding and serial sectioning. In euparal, sections were stained with safranin and alcian. Air-dried flowers and fruits were coated with gold using a JFC-1100 ion-coater for scanning electron microscopy (JEOL, Tokyo, Japan). Early flowers and fruits were photographed with a SteREO Lumar V12 (Carl Zeiss, Jena, Germany) photomicroscope and AxioCam MRc5 digital camera (Carl Zeiss).

Conclusion

Flowers of S. gerrardii are grouped into 20- to 40-flowered open umbellules in a frondo-bracteose inflorescence .The main axis (10–30 cm long) carries 5–14 second-order axes 10–25 cm long The foliage leaves have trilobate to whole (occasionally five-lobate) blades 4–12 cm long on petioles 3–9 cm long. In contrast to the foliage leaves below the inflorescence, which have bigger five-lobate blades up to 25 cm long, these subtending leaves die early. Internodes in the top part of the primary inflorescence axis are shortened. Second-order axes have terminal umbellules and 3–18 third-order axes (5–12 cm long) subtended by minute (4–8 mm long) triangular bracts or infrequently by little foliage leaves with complete lamina 1–3 cm long. Every third-order axis has two prophylls and a terminal umbellule. Anthesis2 causes prophylls to fall off.