Biological and Morphological Aspects of the Velloziaceae Edward S
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Biological and Morphological Aspects of the Velloziaceae Edward S. Ayensu Biotropica, Vol. 5, No. 3. (Dec., 1973), pp. 135-149. Stable URL: http://links.jstor.org/sici?sici=0006-3606%28197312%295%3A3%3C135%3ABAMAOT%3E2.0.CO%3B2-E Biotropica is currently published by The Association for Tropical Biology and Conservation. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/tropbio.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact [email protected]. http://www.jstor.org Wed Jan 23 08:49:56 2008 Biological and Morphological Aspects of the Velloziaceae Edward S. Ayensu Department of Botany, National Museutn of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A. ABSTRACT Recent field and laboratory observations are the basis of a review of various aspects of the biology of the Velloziaceae. Some of the pollinators of the flowers have been identified. Fruit, seed and seedling morphology, rate of germination, phenology, the effect of rainfall on flowering as well as the effect of ecological shift on the habit of the species have been studied. Attention is drawn to the future survival of the Velloziaceae in view of current destruction of the areas in which the plants grow. THE VELLOZIACEAEis one of the most interesting ing of the leaves in response to water loss from the plant families that occurs in Africa and South Ameri- mesophyll. The leaves of most of the South Ameri- ca on account of the difficulties surrounding its ge- can species of Barbacecia do not have furrows, al- neric limits and its distributional pattern. The fam- though a few such as B. irwifziafza have them on the ily contains about 250 species of perennial herbs and abaxial side. Barboceniopsis boliviensis and B. shrubs. The type genus Vellozia Vand. contains vmgusiuna have furrows on both surfaces as do the the largest number of species with approximately Old World species with barbacenioid features (Ayen- 140, followed by Barbacefzia Vand. with about 70. su 1968). Another adaptation against water loss Xerophyta Juss. with about 38 species includes all is revealed by a longitudinal section through the the Madagascan and African species, except for Tal- stem which shows that the bulk of the mass consists botia elegafzs Balfour which occurs in South Africa. of persistent leaf sheaths surrounding a slender The habitats in which the Velloziaceae grow in the woody stem. Apart from the slender stem and its Malagasy Republic, southern Africa, and South lateral branches, there are long aerial roots that are America are more or less similar. Most species are completely encircled by leaf bases. The roots grow lithophytes, growing in stony places such as on ex- down through the entire length of the main stem posed granite rocks, but some are found on dry until they reach the ground, where they spread out plains in alpine environments. For example, among and assume the normal role of anchorage. The long the Brazilian members, Vellozia cafzdida and V. aerial roots grow rather rapidly because the leaf plicata grow on barren soil while Burbacenia par- bases that encircle them help in the maintenance $area prefers humus on rocks. The plants have be- of an ideal microclimate. When the leaf sheaths are come adapted to highly variable climatic conditions, removed from an uprooted Xerophyta, Vellozia or for during the day they are subjected to intense solar Barbace.nia, the aerial roots are especially moist and radiation but occasionally the sunny conditions give may be dripping with water even though the plants way to short but violent rainstorms. At night there are growing in a dry habitat. The water-holding is often dense cloud cover which provides enough capacity of the leaf sheath is demonstrated by re- condensation to moisten the plants and, to a lesser moving one from an herbarium specimen and plac- extent, the substrate. ing it in water or a wetting agent such as Aerosol Many plants in xeric environments have succu- OT Solution (Ayensu 1967). It absorbs the medi- lent leaves which help reduce the rate of transpira- um rapidly as if made of blotting paper. tion as in the cactus-like euphorbias, succulent mela- stomes, and many bromeliads that grow in the same TAXONOMIC REVIEW habitats as the Velloziaceae. The leaves of Vellozii? Earlier authors like Kunth ( 1822 ) confused the Vel- have developed a mechanism for regulating transpir- loziaceae with the Bromeliaceae because of strong ation by the reduction of the rate of water loss per resemblances in habit. The primary classification unit area and/or by the contraction of the transpir- was based on three sets of characters: presence or ing surface area. The rate of transpiration is re- absence of a perianth-tube above the ovary, number duced by the placement of the stomata in abaxial of stamens, and type of filament. Baker (1875) furrows in the leaves. These furrows permit con- and Hutchinson ( 1934) also relied on the presence tractions, inrolling, outrolling, and lengthwise fold- or absence of an extension of the perianth-tube above the ovary as a key character. Although this and Bu~buce?zioides). Almost all species in the sec- reliance is valid at the extremes, it is not infallible. tion Vellozioides occur in Arabia, Malagasy Republic, Pax (1887) used the distinction between six sta- southern Africa, south West Africa, and Nigeria mens and more than six stamens as an important while most species of Bn~bnce?zioik?esoccur in East character. Again such a distinction works well with Africa. most of the species, but it places under Burbaceniu The development of large translucent cells above species that in every other respect are indistinguish- the abaxial sclerenchyma girders and sometimes sub- able from VellozM. It is additionally misleading jacent to the abaxial epidermis along its entire because in some species with nine stamens the petals length is quite common in species of New World subtend a single stamen, as in Bu~buce?zia,whereas Velloziaceae. In the Old World species, such trans- in other spec& they subtend more than one, as in lucent cells are mostly absent, bur in some species Velloziu. Seubert (1847) used the form of the fila- they occur between vascular bundles near the adaxial ment in conjunction with other morphological char- and abaxial epidermal surfaces. The water-holding acters to separate the genera. Basifixed anthers with capacity of translucent cells is well known in various elongate fiiaments were attributed to Vellozia and plants in which such cells occur, and their im- dorsifixed anthers with short filaments assigned to portance may be ascribed to the environmental con- Burbacenia. Smith's classification ( 1962 ) of the ditions to which the plants are subjected (Diogo New World Velloziaceae was essentially a refine- 1926). ment of Seubert's work based on a study of more Floral Anatomy: Unlike the vegetative anatomy, the species. floral anatomv of the Velloziaceae has been little In earlier publications (Ayensu 1968, 1969a, explored, and our general knowledge of the repro- 1969b, 1973) emphasis has been placed upon the ductive anatomy of this family is quite meager. Re- systematic importance of three types of sclerenchyma cently Dutt ( 1970) reviewed the earlier embryologi- patterns associated with the vascular bundles in the cal snidies made by Stenar (1925) on Velloziu ele- leaves. The Vellozia-type refers to species whose gmzs ( =Talbotia ) , Bnrbuce~ziaf i.agru?zs, and Vellozia adaxial sclerenchyma is generally inverted crrscenti- conzpacta. Dutt noted that the embryo sac in Bnr- form or cap-shaped and abaxial sclerenchyma either bnce?ziu. bicolor and Vellozia elegafzr is of the 'Poly- U- or Y-shaped. The Burbuce.~liu-typeis found in gonum' type. One feature of interest is the develop- species where the adaxial side of the vascular bundle ment of an integumentary tapetum formed by the has an inverted Y-shaped sclerenchyma girder and inner integument. Furthermore, he observed that the abaxial girder is either Y-shaped or three-pronged an obturator is developed from the funicle. How- (the flanges of the Y's do not meet directly but ever, Stenar's study lacked details regarding fertiliza- contact is made by thin-walled parenchymatous tion, endosperm development, and embryogeny. cells). The Xerophytu-type occurs in species where On the basis of Stenar's study, Dutt remarked the vascular bundles are accompanied on the adaxial that embryologically the Velloziaceae resemble the side by an inverted crescentiform or V-shaped cap Amaryllidaceae. Of special significance is the de- while the abaxial sclerenchyma is a U- or W-shaped velopment of a funicular obturator in Vellozin gar- cap. Because of recent taxonomic changes (Smith pztrea and the amaryllidaceous species Bo772areu cald- and Ayensu 1974) and further anatomical studies asii.