The wood anatomy of 31 Schefflera species from Indochina, Australia, Oceania, Africa, and South America, 3 species of Didymopanax from South America, and Tupidanthus calyptratus and Scheffleropsis hemiepiphytica from Indochina (Araliaceae) are described. Seven groups of species can be recognised.
The wood anatomy of 22 of the 26 species of Schefflera occurring in New Caledonia was studied. Only two features (the presence of scalariform perforation plates and scanty paratracheal axial parenchyma) appear to be constant throughout the species examined. The pattern of wood structure diversity was analyzed using PCA; the results generally agree with the current recognition of four groups of species among New Caledonian Schefflera based on macromorphology. Three of these groups (Dizygotheca, “Canacoschefflera” and “Gabriellae”) represent natural assemblages closely related to one another. The fourth group (Schefflera sect. Schefflera) is isolated from the others, as indicated by its very large rays and abundant septate fibres. The occurrence of crystals in chambered cells of axial parenchyma was observed for the first time in Araliaceae. The wood structure of Schefflera plerandroides, previously placed in the segregate genus Octotheca, shows no essential differences from that of the other members of the Dizygotheca group, supporting the hypothesis that polymerous flowers have evolved independently at least twice within the Schefflera alliance.
The taxonomic position of fossil woods suggested to be related to Bischofia is reassessed based on the examination of the wood anatomy of recently collected samples of its two modern species (B. javanica and B. polycarpa). Woods of B. palaeojavanica from the middle Pliocene of India, and B. javanoxyla from the early Miocene of northern Taiwan have features of extant B. javanica. In contrast, the Eocene Bischofia maomingensis (South China) differs from Bischofia in a number of features and we propose a new combination Chadronoxylon maomingensis (Feng et Jin) Oskolski, Stepanova, Huang et Jin. Bischofia palaeojavanica from the latest Cretaceous–earliest Paleocene Deccan Intertrappean Beds, India, and all other pre-Miocene woods assigned to Bischofia differ from extant Bischofia in vessel diameters, vessel element lengths, intervessel pit sizes, position of vessel-ray pits, and/or abundance of sheath cells in rays. Therefore, their generic position must be reconsidered, and there is no reliable record of Bischofia wood older than Miocene.
A gymnosperm wood is described from the Oligocene-Miocene of Hainan Island, South China. It is characterized by circular, thin-walled tracheids with resin plugs, 1–3-seriate alternate or opposite intertracheary pits in radial walls, 1–2-seriate rays, cross fields with 3–14 araucarioid cross-ﬁeld pits. These are features found in the Araucariaceae and the fossil is designated as Agathoxylon sp. Fossil woods with anatomical characteristics seen in the Araucariaceae are extremely rare in the North Hemisphere after the K/T boundary. Thus, this Agathoxylon from the Oligocene-Miocene of South China has significance for biogeographic studies.
This paper describes a new species of fossil wood, Wataria yunnanica Li et Oskolski, from the Dajie Formation of the middle Miocene in southern Yunnan province, China. This species shows the greatest similarity to the modern genus Reevesia Lindl. from the subfamily Helicteroideae of Malvaceae. The fossil specimen is ascribed to the genus Wataria Terada & Suzuki based on its combination of ring-porous wood and the presence of tile cells. It differs from other Wataria species because vessel groups are common in its latewood. This is the first record of Wataria in China. Other species of this genus have been reported from Oligocene and Miocene deposits in Japan, and from Miocene deposits in Korea. The occurrence of ring-porous wood in the Dajie Formation suggests that there may have been a seasonal (probably monsoonal) climate in southern Yunnan during the middle Miocene.
The wood structure of two related African genera, Cussonia Thunb. (15 of 21 species) and the monotypic Seemannaralia R.Vig. (Araliaceae) is examined. The considerable diversity in wood anatomical characters within these taxa is mostly related to environmental factors; taxonomic groupings or phylogenetic relationships seem to be less important. The shortening of vessel elements and fibres, an increase in vessel number per group, a decrease in vessel diameter and a reduction in the number of bars of perforation plates, are associated with the more temperat species. The changes in vessel grouping show a significant correlation with rainfall. The placement of the simple-leaved Cussonia species in the subgenus Protocussonia and the isolated position of C. paniculata Eckl. & Zeyh., the only member of the subgenus Paniculatae, are supported. Many Cussonia species share a very low fibre to vessel element length ratio. Despite the basal position of Seemannaralia relative to Cussonia revealed by molecular data (Plunkett et al. 2004), its wood structure is more specialised in terms of the Baileyan major trends in wood evolution. This discrepancy may be the effect of a long-term adaptation of tropical ancestors of Seemannaralia to drier biomes.
Wood anatomy of Buddleja is well-explored but not in many southern African members, which form a grade of species and small clades that form successive sister groups to the rest of the genus, and its bark structure has not been studied at all. We provide new descriptions of wood anatomy for twelve species, including nearly all Buddleja from southern Africa and two species of Freylinia in the sister group of Buddleja. We also describe bark structure from fifteen species. To assess if wood anatomy provides phylogenetic and/or ecological signal, we compiled data on wood traits and climatic variables from the distributions of 53 species. Wood traits counteracting cavitation correlated with higher temperature and precipitation seasonality; simultaneously they were better expressed in species with smaller maximal plant height. It is likely that hotter and drier areas harbour smaller plants which have traits conveying higher conductance safety. Bark structure varies considerably. In bark of Buddleja section Gomphostigma, periderm is initiated in the outer cortex and develops thin-walled phellem, and sclerification of their phloem does not occur. This resembles bark in Freylinia, supporting the position of section Gomphostigma as sister to the rest of Buddleja. In the remaining Buddleja species, bark is characterised by formation of periderm with phelloid cells in the secondary phloem. The phellem is often uniseriate, a condition not reported elsewhere. Its formation occurs close in time to solid sclerification of the cut-off phloem, suggesting a possible novel ontogenetic mechanism.
A remarkable, almost fur-like “indumentum” of velvety “hairs” (sometimes referred to as “fungi”) occurs on the roots (and to a lesser extent also on the trunk) of Lannea schweinfurthii var. stuhlmannii and is known as vhulivhadza in the Venda language (Tshivenḓa). The hairs are traditionally used by the Venda people (Vhavenḓa) of the Limpopo Province of South Africa, for various biocultural purposes. A detailed anatomical study of the origin, structure and development of these unusual “hairs” showed that they are of peridermal origin and develop from dense clusters of phelloid cells which are scattered within the stratified phellem. These cells are capable of considerable radial elongation thus forming hair-like radial files of elongated phelloid cells. The “hairy” patches on the bark may also develop from lenticels which become hypertrophied. These clusters of phelloid cells resemble the hyperhydric tissue which is reportedly formed in periderm of stems exposed to a water-saturated environment in some plant species. The formation of hyperhydric-like tissue in roots and stems of L. schweinfurthii var. stuhlmannii occurs, however, under relatively arid conditions. Since this tissue contains large intercellular spaces, it may also be regarded as a specialized type of aerenchymatous phellem. The adaptive significance, if any, of the phelloid “hairs” remains unknown.
The wood and bark structure of Leucosidea sericea and two species of Cliffortia, the South African members of the tribe Sanguisorbeae (Rosaceae) are described. These two genera share few anatomical traits (the presence of schizo-rhexigenous intercellular spaces in the cortex, almost exclusively simple perforation plates, small alternate intervessel pits, etc.) with other Rosaceae. However, Leucosidea shows a distinct storied structure of the secondary phloem and wood as well as stratification of the secondary phloem, with conductive elements and nonsclerified crystalliferous axial parenchyma arranged into alternating bands. These conditions are recorded for the first time for the family Rosaceae. In contrast to Leucosidea, two species of Cliffortia show neither storied structure of secondary phloem and xylem, nor stratification of secondary phloem.