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doi: 10.1111/j.1095-8339.1997.tb02243.xpmid: N/A
AbstractAbnormal megaspore tetrad configurations from Selaginella laevigata and of Lagenicula crass-iaculeata (Lower Carboniferous) have been studied by SEM. These abnormalities reflect the variation expected in the presumed evolution of the seed-plants from free-sporing het-erosporous ancestors. In addition, they indicate a possible role for the aborted members of a tetrad in the successful development and maturation of the functional spore(s). Aborted members of tetrads also reveal the later stages of the developmental sequence occurring in spore wall construction and highlight the interplay of sporopollenin production, its colloidal flocculation and polymerization, and distortion caused by protoplast expansion. Possible causes of abortion in both living and extinct lycopsid megaspores are discussed.
VANZELA, A. L. L.; RUAS, P. M.; MARIN-MORALES, M. A.
doi: 10.1111/j.1095-8339.1997.tb02244.xpmid: N/A
AbstractKaryotype studies in eight species of Dalechampia, including 10 natural populations, revealed chromosome numbers (2n = 36, 46, 138 and 198) differing from two numbers cited in the literature (2n = 44 and 72). The basic number x = 6, as in the genus Acalypha, may be considered ancestral in Dalechampia. Analysis of chromosome number, haploid chromosome length and karyotype symmetry suggests that the major chromosome mechanism acting in karyotype evolution of Dalechampia is polyploidy, but differences in chromosome morphology may be caused by chromosome rearrangements.
doi: 10.1111/j.1095-8339.1997.tb02245.xpmid: N/A
AbstractA new Polystichum (Pteridophyta: Dryopteridaceae) species, P. incongruum J.P.Roux sp. nov. from the Western and Eastern Cape Provinces from Soudi Africa is described. This variable species is related to P. pungens (Kaulf.) C.Presl but differs from it in pinnule morphology, the frequent occurrence of glandular cells along the sporangium stalk, the (more rare) occurrence of clavate unicellular glands along the indusium margin and a chromosome number of 2n = 164.
doi: 10.1111/j.1095-8339.1997.tb02246.xpmid: N/A
AbstractLeaf exudates from individuals of 29 species included in Aloe Section Pachydendron have been separated by TLC and HPLC to reveal their phenolic components. All the zones are described by their chromatographic behaviour and UV absorption properties, but not all can be identified as known compounds so are distinguished by an arbitrary code. Section Pachydendron has been shown to be chemically heterogeneous although there are some correlations between species said to be taxonomically related. Without attaching taxonomic significance four chemical groupings can be discerned: (1) species in which chromones are prominent; (2) species in which anthrone and anthraquinone glycosides are prominent; (3) species containing mainly purple-staining phenolic compounds; and (4) species with few leaf exudate phenolic compounds. This survey emphasizes the uncertain taxonomy of the Section and the need for more extensive collection and analysis.
doi: 10.1111/j.1095-8339.1997.tb02247.xpmid: N/A
AbstractOf the 13 genera and 600 species of the subdivision Calamoideae, only four genera—Calamus, Daemonorops, Korthalsia, and Plectocomia—represent the Indian rattans which are found in three major regions: Western Ghats of Peninsular India, Andaman and Nicobar islands and north and north-eastern India. Detailed anatomical survey of 42 species shows considerable differences among the four genera. The vascular bundle in Calamus, Daemonorops and Korthalsia is characterized by a solitary metaxylem vessel and two phloem fields, while Plectocomia shows 1–2 metaxylem vessels and a single phloem field. The mechanical tissues show diversity in Korthalsia and Plectocomia with sclereids as a yellow cap on the outer side of the fibrous sheaths of vascular bundles. The size of the different cells, the diameter of the metaxylem vessel in particular, appears to be related to species habit, geography and stem size. The Andaman and Nicobar islands with equable temperature and high humidity provide the best environment for cane growth—the widest vessels are in canes from this region. While altitudinal influence on vessel diameter appears to be relatively small, the higher latitude is associated with narrow and short vessel elements. With the exception of C. erectus, an erect species with the thickest stem, vessel diameter shows positive correlation with stem diameter. Vessel perforations are simple or rarely scalariform. Climbing palms which grow to enormous heights generally have wider vessels with simple perforations, an adaptation for conductive efficiency. Based on these results, the implications of stem anatomy for rattan biogeography, systematics and identification are discussed, and identification keys to species presented.
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