On the homology of the scales in Gunnera (Gunneraceae)

Abstract

In the genus Gunnera, the species of subgenus Panke are unique in having large, triangular scales between the leaves on the rhizomes. The morphological significance of these scales has been extensively debated in the past. They have been interpreted as stipules, ligules, or cataphylls, with attempts made to identify homologous structures in representatives of the other subgenera. In the stoloniferous subgenus Misandra, the shoot apex is covered by a hoodlike structure, usually termed ochrea, generally considered homologous to the scales in Panke. Efforts to find similar structures in the remaining subgenera were unsuccessful. Due to the lack of a phylogenetic hypothesis, the homology of the scales has remained unresolved. In this study, the shoot apices of species from all subgenera were examined by light and scanning electron microscopy and the results interpreted in a phylogenetic context. The tip of the stolons in subgenera Pseudogunnera and Milligania carries two opposite cataphylls at the base of the new shoot. These are homologous to the ochrea in Misandra which is in turn homologous to the scales in Panke; the latter are thus neither stipules nor ligules but cataphylls. The stems of subgenera Ostenigunnera and Gunnera have no similar structures. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 301−308.

Intra-individual variation of flowers inGunnerasubgenusPanke(Gunneraceae) and proposed apomorphies for Gunnerales

“…The two lateral stipules and the ligule on the adaxial base of the petiole (‘Kapuze’ sensu Puff, 1978) in Myrothamnus might be homologous to one (or more) of the following structures in Gunnera : (1) the tooth‐like sheath lobes present in foliage leaves of G. herteri (Rutishauser et al. , 2004); (2) the opposite cataphylls present in species of subgenera Milligania and Pseudogunnera (Skottsberg, 1928, 1930; Wanntorp, Wanntorp & Rutishauser, 2003); (3) the ligule at least in G. macrophylla (Skottsberg, 1930), (4) the ochrea in the species of subgenus Misandra (Wanntorp et al. , 2003); or (5) the complex lepidophylls in the species of subgenus Panke , interpreted as stipules (Reinke, 1873; Berckholtz, 1891; Schnegg, 1902; Goebel, 1905; Glück, 1919, among others), intravaginal scales (Troll, 1939) or cataphylls or scale leaves (Skottsberg, 1928; Mora‐Osejo, 1984, 1995; Mora‐Osejo et al.…”

“…, 2003); or (5) the complex lepidophylls in the species of subgenus Panke , interpreted as stipules (Reinke, 1873; Berckholtz, 1891; Schnegg, 1902; Goebel, 1905; Glück, 1919, among others), intravaginal scales (Troll, 1939) or cataphylls or scale leaves (Skottsberg, 1928; Mora‐Osejo, 1984, 1995; Mora‐Osejo et al. , 2009; Wanntorp et al. , 2003).…”

Biological Flora of theBritishIsles:Gunnera tinctoria

“…600 km off the coast of Chile, where seeds from mainland Chile may have arrived via the digestive system of birds (Pacheco et al . ; Wanntorp, Wanntorp & Rutishauser ).…”

“…Gunnera tinctoria belongs to the subgenus Panke (Molina) Schindler, which includes large species with at least some hermaphroditic flowers (Fuller & Hickey 2005). This subgenus is mostly restricted to the Andean cordillera Wanntorp, Wanntorp & Rutishauser 2003). Based on morphological and flavonoid analyses, G. tinctoria appears to be the closest ancestor to three Gunnera species of Panke found on the Juan Fernández Islands, located c. 600 km off the coast of Chile, where seeds from mainland Chile may have arrived via the digestive system of birds (Pacheco et al 1993;Wanntorp, Wanntorp & Rutishauser 2003).…”

“…The earliest pollen record of Gunnera (Tricolpites reticulatus) is from the Turonian (c. 90 Ma) in South America (Wanntorp, Praglowski & Grafström 2004). Wanntorp et al (2001) and Wanntorp, Wanntorp & Rutishauser (2003) showed that Gunnera can be considered of Gondwanan origin and was widespread and abundant in North America from the Late Cretaceous to the Eocene (80-50 Ma), although its distribution has retreated over time, probably due to climatic and environmentally related changes (Jarzen 1980;Osborne & Sprent 2002;Osborne & Bergman 2009), particularly increases in aridity and the disappearance of inland seas and seaways that were common during the Cretaceous period (Osborne & Sprent 2002).…”