Leaf anatomy in a Venezuelan montane forest

A survey has been made of the leaf anatomy of 43 woody species in three montane vegetation types of Isla Margarita, Venezuela, differing in levels of cloud cover (and hence wetness) and exposure to wind. The only character that varies significantly with increasing probability of periodic drought is specific leaf area, which can be related to the higher proportion of deciduous species in the drier habitat. Leaves become significantly smaller and thicker with increased exposure to wind, and have thicker outer epidermal walls and cuticles. Most characters, including stomatal density, guard cell length, palisade: non-palisade ratios, and the incidence of such features as hypodermis, sclerenchyma, crystals and secretory structures are highly variable and show few or no trends according to habitat. Some of these characters are apparently more constrained by phylogeny than by immediate ecological circumstances. As a contribution to the continuing debate on the significance of xeromorphy in tropical montane forest leaves, it is suggested that low light levels due to cloud cover can be discounted as an important determining factor; in the case of the Isla Margarita vegetation, the need to avoid excessive leaf temperatures may be of greater significance.     

Vegetative diversification and radiation in subtribeDendrobiinae (Orchidaceae): Evidence from chloroplast DNA phylogeny and anatomical characters

The data derived from a chloroplast DNA restriction site analysis of subtribeDendrobiinae (Orchidaceae) indicate that extreme vegetative diversification is concentrated in two limited parts of this group. Overlaying the vegetative character states onto the chloroplast DNA cladogram suggests that several xeromorphic, vegetative characters evolved in the lines leading to the above-mentioned clades. Several anatomical characters are also associated with xeromorphy. These vegetative and anatomical characters facilitated the establishment of this group in various dry habitats. On the other hand, the modifications of size and number of parenchymatous cells substantially contributed to the vegetative diversification. This fact implies that a simple structural adjustment can result in a major modification of growth habits in theDendrobiinae.     

An ecological interpretation of the difference in leaf anatomy and its plasticity in contrasting tree species in orange kloof,table mountain,South Africa

Leaf anatomy and morphology were studied in 11 tree species growing in an undisturbed forest and the adjoining fynbos for over 50 years. Functional anatomical results suggest that the forest and the fynbos are ecologically distinct. Moreover, leaf anatomy suggests that the foliage is primarily adapted for photosynthesis rather than for control of transpirational water loss. Forest precursor tree species and scrub species exhibit xeromorphy in the fynbos whereas they exhibit mesomorphic features inside the forest. The wide-ranging species, such as Olea capensis subsp. capensis, simulated the response of the forest precursors, with the cuticle being phenotypically plastic between the forest and the fynbos but not between the stream and non-stream habitats. Finally, the forest precursors, the scrub species, and the wide-ranging taxa seem to have anatomical characters which can be modified in the fynbos and therefore allow its colonization by a variety of different species.     

Cuticular morphology and aspects of the ecology and fossil history of North Queensland rainforest Proteaceae

Cuticles of North Queensland rainforest Proteaceae were examined using light and scanning electron microscopy. The genera of North Queensland rainforest Proteaceae are mostly endemic and composed of one or few species, with greatest diversity in the granitic uplands of the region. Knowledge of cuticular morphology may be an important tool in determining the true affinities of several undescribed taxa in the region and can be used to explore hypotheses relating to the history of the Proteaceae. Some species exhibit purported xeromorphic features of thick cuticles, sunken stomates and dense trichome cover on the abaxial surface. Grevillea , Banksieae and Stenocarpus are believed to have radiated into open, much less mesic environments. In the former two taxa this can be interpreted in terms of xeromorphic features expressed in their cuticular morphologies, whereas in Stenocarpus amphistomaty in species of open habitats suggests an alternative mode of evolution more related to physiological factors. Several Cainozoic proteaceous macrofossils temporally and spatially far removed from North Queensland possess cuticular morphologies very similar or identical to extant rainforest taxa in the region.     

Taxonomic, evolutionary and ecological implications of the leaf anatomy of rhizomatous Iris species

The leaf anatomy of the rhizomatous Iris species with ensiform leaves and the related genera Pardanthopsis and Belamcanda is described. Their isobilateral leaves may or may not have a pseudo-dorsiventral structure. Variable characters of their leaf blades include: outline in transverse section, height and shape of papillae, form and structure of stomata, transverse section outline of marginal fibre strands and sclerenchy matous inner bundle sheath at phloem and xylem poles, forms of mesophyll arrangement, mesophyll structure and air canals, vascular bundle arrangement and the detailed structure of the larger vascular bundles, distribution of tannin, size and distribution of crystals. The taxonomic and ecological significance of these characters has been evaluated.
The anatomical characteristics of 25 supraspecific taxa in three genera are presented and compared in tables. The relationships and evolutionary position of these taxa are discussed. Each of the three subgroups within Iris appears to be correlated with a syndrome of anatomical characters. Some species currently of uncertain taxonomic position are discussed, and their classification based on anatomical data is suggested.
Some characters related to xeromorphy or helomorphy are mentioned.     

Leaf and twig anatomy of Eriope, a xeromorphic genus of Labiatae

The leaf and twig anatomy of 25 species of the genus Eriope were studied. The twig anatomy is very uniform apart from the level of formation of early layers of cork. Leaf anatomy shows considerable variation between the species, and this is correlated to some extent with the extreme habit range from trees to woody herbs. Characters of the lamina that show variation are: trichome type and frequency, cuticular markings, leaf dorsiventral or isobilateral, presence of adaxial stomata, presence of a hypodermis, number of layers of adaxial palisade mesophyll cells, occurrence of large bundles of phloem fibres at main veins, type of areolation and marginal venation. Petiole vasculature is simple and generally with either four distinct vascular bundles or two vascular arcs. The most xeromorphic species are usually woody herbs or sub-shrubs, and tend to have thick, isobilateral leaves with large bundles of phloem fibres and few hairs, or strongly dorsiventral leaves with a hypodermis and stomata in deep abaxial hair-lined depressions. The correlation of xeromorphic characters with environmental conditions is discussed. Leaf anatomy is of limited value in elucidating relationships within the genus.     

Leaf anatomy of the subtribe Hyptidinae (Labiatae)

The leaf anatomy of the subtribe Hyptidinae (Labiatae), which consists of four small genera and the largr genus Hyplis , is dercribed. The leaves may be dorsiventral or isobilateral. Variable characters of the lainina include: frequency and forms of trichomes, cuticular markings, presence of adaxial stoinata, thickness of leaf, thickness of adaxial epidermis, presence of a hypodermis, occurrence of sclcrified tissues (especially sclerified bundle sheath extensions, phloem and xylem fibres), mesophyll structure and venation pattern. Petiole vasculature varies from simple to complex, sometimes with medullary traces present. Most of the variable characters are related to xeromorphy and are tax-onomically useful within the framework of the present classification.