Wood and bark anatomy of Steganotaenia and Polemanniopsis (tribe Steganotaenieae, Apiaceae) with notes on phylogenetic implications

Abstract

The wood and bark structure of the distinctive southern African genera Polemanniopsis (including the newly described species P. namibensis) and Steganotaenia have been described. To allow for comparisons with the traditional subfamily Saniculoideae, a shrubby species of Eryngium from the Juan Fernández Islands was also studied. Polemanniopsis and Steganotaenia were recently considered as two closely related genera forming a new tribe Steganotaenieae of subfamily Saniculoideae (Apiaceae), whereas Eryngium is commonly recognized as a member of Saniculoideae. Eryngium differs significantly from the other two genera in the smaller size of intervessel pits, sclerification and radial dilatation in collapsed secondary phloem, the absence of crystals in the phelloderm cells and the occurrence of druse crystals in secondary phloem ray cells. Steganotaenia and Polemanniopsis share features, including the presence of marginal axial parenchyma, the occurrence of radial secretory canals in secondary xylem, dilatation of the secondary phloem by axial parenchyma stretching, cortical periderm initiation and the presence of chambered phelloderm cells containing druse crystals. These characters (especially the occurrence of chambered crystalliferous cells in phelloderm, which has not yet been reported for Apiaceae) support both the monophyly and the isolated position of the Steganotaeniae. No reliable synapomorphic features could be found to support a relationship with Saniculoideae. Steganotaenia is remarkable in the presence of axial secretory canals in the phelloderm: these structures have not yet been found in the periderm of any member of Apiales. Our results do not provide any support for the suggestion that the woody habit in the three genera examined was derived from herbaceous ancestors secondarily.

The systematic significance of bark structure in southern African genera of tribe Heteromorpheae (Apiaceae)

“…Anginon , Dracosciadium , Glia , Heteromorpha and Polemannia show the presence of secretory canals in the cortex (Figs 6–8) and secondary phloem (Figs 18, 19, 21), the presence of two types of axial parenchyma (sheath parenchyma surrounding secretory canals and phloem parenchyma accompanying sieve tubes) and the absence of fibres in the secondary phloem. These bark characters are typical of the large majority of woody Apiaceae and all Araliaceae, Myodocarpaceae and Pittosporaceae (Van Tieghem, 1884; Metcalfe & Chalk, 1950; Kotina & Oskolski, 2010; Nilova & Oskolski, 2010; Oskolski et al ., 2010) examined to date (Fig. 22), with the exception of Centella L. (Mackinlayoideae, Apiaceae), which has no secretory canals in the secondary phloem.…”

“…examined to date, whereas Steganotaenia Hochst. and Polemanniopsis B.L.Burtt belonging to tribe Steganotaenieae (subfamily Apioideae) are distinctive in having a diffuse type of secondary phloem dilatation (Kotina & Oskolski, 2007; Nilova & Oskolski, 2010; Oskolski & Van Wyk, 2010; Oskolski et al ., 2010). As for other families, the radial type of dilatation occurs throughout Pittosporaceae (Nilova & Oskolski, 2010), in most Myodocarpaceae and in early branching lineages of Araliaceae and in the Polyscias J.R.Forst.…”

“…The aim of this paper is therefore to describe bark structural characters of the woody members of Heteromorpheae from southern Africa and to assess their usefulness in systematics at all taxonomic levels. This work is part of a general study of the diversity and evolution of bark structure in Apiales (Kotina & Oskolski, 2007, 2010; Nilova & Oskolski, 2010; Oskolski & Van Wyk, 2010; Oskolski, Rossouw & Van Wyk, 2010).…”

A comparison of paraffin and resin‐based techniques used in bark anatomy

“…Although bark is one of the most conspicuous features of woody plants in the field, and despite several studies having shown its potential for improving phylogenetic relationships in many plant families (e.g., Metcalfe & Chalk, 1950a, b;Zahur, 1959;Esau, 1969;Richter, 1981;Roth, 1981;Esau & Cheadle, 1984;Archer & Van Wyk, 1993;Liu & Gao, 1993;Costa & al., 1997;Carlquist, 1991Carlquist, , 1996Carlquist, , 1998Carlquist, , 2005De Magistris & Castro, 2001;Castro & al., 2005;Olson, 2005;Schweingruber, 2006;Junikka & Koek-Noorman, 2007;Oskolski & al., 2007Oskolski & al., , 2010, bark is still one of the most poorly known plant tissues and therefore rarely included in systematic studies. There are three major reasons for the fragmentary knowledge of bark anatomical data.…”

Island plants, comparative morphology and genetic integrity

“…The power of this type of approach, either alone or linked to molecular phylogenetics, in helping to develop our understanding of the relationships between plants is illustrated well by subject matter published recently in the Botanical Journal of the Linnean Society . Papers published cover extant groups of angiosperms (Banks, Himanen & Lewis, ; Bradshaw et al ., ; Carlquist, ; De Villiers, Tilney & Van Wyk, ; Lu et al ., ; Oskolski, Rossouw & Van Wyk, ; Pole, ; Ren, Chang & Endress, ; Xu & Ronse De Craene, ; Matthews & Endress, ; Zhang & Ren, ), gymnosperms (Rydin, Khodabandeh & Endress, ) and pteridophytes (Christenhusz, ; Lehtonen et al ., ) and extinct fossil taxa (Seyfullah et al ., ; Edwards & Axe, ). An earlier issue this year (with an editorial by Schönenberger & Von Balthazar, ) included several additional papers of this type.…”