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Journal ArticleDOI

Anatomy of the Dicotyledons.

About: This article is published in American Midland Naturalist.The article was published on 1950-11-01. It has received 2511 citations till now.
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01 Jan 1998
TL;DR: The stem revealed anomalous secondary growth characterised by the development of successive rings of xylem and phloem by the cambium exclusively composed of fusiform initials giving rise to rayless secondary vascular tissues.
Abstract: Structure of vascular cambium and its derivatives in Boerhaavia diffusa L., B. verticillata Poir. and B. rependa Willd. (Nyctaginaceae) was studied by anatomical methods.The stem revealed anomalous secondary growth characterised by the development of successive rings of xylem and phloem. The cambium was exclusively composed of fusiform initials giving rise to rayless secondary vascular tissues. While undergoing periclinal divisions cambium appeared nonstoried but remained storied when the divisions ceased. Each successive ring of cambium was originated from the outermost phloem parenchyma cells. The cambial ring was functionally segmented into fascicular and interfascicular regions, the former mainly producing conducting elements of xylem and phloem and the latter giving rise to parenchyma cells. The parenchyma cells on the xylem side developed into conjunctive tissue following thickening and lignification of cell walls. However, in B. verticillata and B. rependa the parenchyma cells on the pholem side also became lignified. In B. diffusa parenchyma cells did not undergo lignification. As a result, alternate bands of lignified and parenchyma bands became distinct in the stem. Vessel elements were short with simple perforation plate on slightly oblique to transverse endwall. Sieve tube members were slightly shorter as compared to the fusiform cambial cells.

22 citations

Journal ArticleDOI
TL;DR: The Gentianales as circumscribed by Benson, Cronquist, Dahlgren, Goldberg, Hey wood and al., Melchior, Stebbins, Takhtajan and Thorne is investigated and a consensus classification or classificatory model for the order is proposed.
Abstract: The Gentianales as circumscribed by Benson, Cronquist, Dahlgren, Goldberg, Hey wood et al., Melchior, Stebbins, Takhtajan, and Thorne is investigated. From these a consensus classification (not in the cladistic sense) or classificatory model for the order is proposed. This classification is discussed, as are the relationships of the taxa within it. Excluded taxa are also discussed. In particular, the Apocynineae is examined in detail and it is pointed out that for this suborder the present consensus classification, at the family level, is congruous only if the taxa involved are monophyletic. Data are then supplied to show that, as yet, neither monophyly nor paraphyly can be proved conclusively for the taxa of the Apocynineae.

22 citations

Journal ArticleDOI
TL;DR: The stem and leaf anatomy of seven species of Curtia and Hockinia montana are described and it is suggested that these anatomical characteristics are potentially useful for clarifying the taxonomy of Gentianaceae.
Abstract: The delimitation of species and even support of the genera Curtia and Hockinia, monotypic genus, are still controversial. To define anatomical characteristics that help resolve taxonomic problems, the stem and leaf anatomy of seven species of Curtia and Hockinia montana are described. Some characteristics are found in both genera: leaves with uniseriate epidermis, dorsiventral mesophyll, cells of the palisade parenchyma with invaginations, basal acrodromous venation with an incomplete marginal ultimate venation, presence of colleters and nectaries, stem with small wings and internal phloem. The types of stomata, the midrib vascular bundle, and the type and distribution of nectaries were used to separate the genera. The presence/absence of crystals, the sinuosity of the anticlinal walls of the epidermal cells, the type and distribution of stomata, and the distribution of nectaries distinguish species of Curtia. Our results suggest that these anatomical characteristics are potentially useful for clarifying the taxonomy of Gentianaceae, and that they represent an additional tool for distinguishing genera and identifying species of Curtia, particularly pointing out the need to revise the synonymy between C. patula and C. tenuifolia. We also highlight the first report of leaf nectaries and colleters in the Saccifolieae and the first record of stem nectaries in the Gentianaceae.

22 citations

Journal ArticleDOI
TL;DR: Analysis of 26S rDNA sequences suggests that Cuscuta is a derived member of Convolvulaceae, which would place it within the Solanales or within the Polemoniales.
Abstract: Cuscuta is a parasitic angiosperm that has been considered alternatively either as a genus within Convolvulaceae or as a monogeneric family in its own right. Although typically placed in the Solanales,Cuscuta has also been positioned within the Polemoniales. Extreme reduction of morphological and anatomical characters, as well as chloroplast genome reductions and rearrangements, has made the phylogenetic placement ofCuscuta uncertain. Analysis of 26S rDNA sequences suggests thatCuscuta is a derived member of Convolvulaceae. Molecular results are discussed in relation to the morphological and anatomical characters of autotrophic members of Convolvulaceae.

22 citations