43 research outputs found
Comparative vegetative anatomy and systematics of Oncidiinae (Maxillarieae, Orchidaceae)
Subtribe Oncidiinae comprises a vegetatively heterogeneous assemblage of species that has persistently been incapable of organization. Anatomy was considered to be a possible means to resolve the perplexity of relationships amongst the constituent taxa. The consistent occurrence of a foliar hypodermis, homogeneous mesophyll, conical silica bodies in stegmata, and ubiquitous fibre bundles in leaves provides a matrix for linking the taxa, as do the parenchymatous pith and O-thickened endodermal cell walls in roots. However, the strict consensus of the 40 genera studied was completely unresolved, suggesting that vegetative characters alone are insufficient to assess the relationships amongst these taxa, a conclusion also reached for the remainder of Maxillarieae
Comparative vegetative anatomy and systematics of Oncidiinae (Maxillarieae, Orchidaceae)
Subtribe Oncidiinae comprises a vegetatively heterogeneous assemblage of species that has persistently been incapable of organization. Anatomy was considered to be a possible means to resolve the perplexity of relationships amongst the constituent taxa. The consistent occurrence of a foliar hypodermis, homogeneous mesophyll, conical silica bodies in stegmata, and ubiquitous fibre bundles in leaves provides a matrix for linking the taxa, as do the parenchymatous pith and O-thickened endodermal cell walls in roots. However, the strict consensus of the 40 genera studied was completely unresolved, suggesting that vegetative characters alone are insufficient to assess the relationships amongst these taxa, a conclusion also reached for the remainder of Maxillarieae
Vegetative anatomy and systematics of Triphorinae (Orchidaceae)
Triphorinae represents a group of three anatomically simple genera, the structural features of which are unspecialized. The anomocytic stomatal pattern occurs in all genera; it predominates in Triphora . A foliar hypodermis, sclerenchyma, fibre bundles and stegmata are absent. The mesophyll is homogeneous. The exodermal and endodermal cells in the roots are entirely thin-walled and tilosomes are absent. However, there are anatomical modifications that appear to be unique: root hairs in Monophyllorchis are borne on velamenal buttresses and, in Psilochilus , they arise endogenously. In the root vascular system of Psilochilus , the metaxylem occurs as a circumferential band. The surfaces of stems in Triphora are tuberculate. Mycorrhizae appear to characterize the root cortices of all genera
Comparative vegetative anatomy and systematics of Laeliinae (Orchidaceae)
Laeliinae are one of the most prominent orchid subtribes, with c. 40 genera and nearly 1500 species, and contain a disparate group of taxa with widely varying morphological features. There does not appear to be a complex of characters to which one can refer in order to delineate the subtribe as a whole. Thus, it was thought that vegetative anatomy might provide clues to the monophyly of the group. The microscopic structure of the leaves, stems and roots of representatives of most of the genera was studied. It was concluded that the anatomy lacks overall uniformity and that vegetative characters alone are insufficient to assess the relationships amongst the genera. The only nearly consistent anatomical feature was the abaxial row of fibre bundles in the leaves. Thus, anatomically, as well as morphologically, Laeliinae are a mixed bag
Systematic and comparative anatomy of Maxillarieae (Orchidaceae), sans Oncidiinae
On the basis of floral and vegetative morphology, 63 tropical American genera have been recognized within Maxillarieae. We were able to examine anatomical material of all subtribes, excluding Oncidiinae. Stegmata with conical silica bodies occur in leaves and stems of all subtribes excluding Ornithocephalinae, and pericyclic stegmata found in roots are characteristic of Lycastinae. Lycastinae and Maxillariinae are characterized by foliar glands, foliar fibre bundles and tilosomes. Endodermal cells are U-thickened in most Zygopetalinae; O-thickened in most Lycastinae, Ornithocephalinae and Telipogoninae; variously thickened in Maxillariinae; and thin-walled in Cryptarrhena lunata. Water-storage cells varied from thin-walled to variously banded throughout Maxillarieae. Cladistic analyses using anatomical characters yielded no resolution among subtribes, illustrating that anatomical characters are of limited value in assessing relationships within this tribe