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11777 results in Plant sciences

Page 36 of 589

  • 56 - Elatinaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 560-560

  • Summary

    Small, more or less aquatic annuals or rarely perennials. Leaves opposite, simple, entire, more or less petiolate, with stipules. Flowers minute, solitary in leaf axils, bisexual, hypogynous, actinomorphic. Sepals 3–4, membranous, free or united at base. Petals 3–4, free. Stamens 6 or 8. Styles 3 or 4, very short; stigmas capitate. Ovary 3- to 4-celled, each with numerous ovules on axile placentation. Fruit a 3- to 4-celled capsule.

    Contains 2 genera and about 40 species; cosmopolitan.

    Elatine L.

    Annual or perennial herbs in wet places. Leaves opposite, simple, entire, with stipules. Flowers minute, solitary in leaf axils or in cymes, bisexual, hypogynous, actinomorphic. Sepals 3–4. Petals 3–4, reddish or pinkish-white. Stamens 6 or 8. Styles 3 or 4; stigmas capitate. Fruit a 3- to 4-celled capsule.

  • 45 - Corylaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 355-364

  • Summary

    Deciduous, monoecious trees or shrubs. Buds with scales. Leaves alternate, simple; stipules caducous. Flowers in unisexual anemophilous catkins. Male catkins pendulous, with one flower in the axil of each bract; bracteoles 2, united with the bract, or absent; perianth absent; stamens 3–14. Female catkins of 2 flowers in the axil of each bract; bracteoles present; perianth small, irregularly lobed; ovary with 2 loculi, inferior; styles 2. Fruit a nut, subtended or surrounded by an involucre formed from the accrescent bract and bracteoles.

    Contains 4 genera and over 50 species in north temperate regions and central America.

  • Buds ovoid, obtuse at apex; leaves usually with 5–12 pairs of veins; fruits in clusters of 1–10 3. Corylus

  • Buds fusiform to ovoid, acute at apex; leaves with 9 or more pairs of veins; fruits numerous, in pendulous spikes 2.

  • Bark grey, generally smooth; male catkins appearing in spring; nuts subtended by a 3-lobed or serrate involucre 1. Carpinus

  • Bark becoming scaly and rough; male catkins visible throughout the winter; nuts enclosed in an entire, bladder-like, apiculate involucre 2. Ostrya

    • Carpinus L.

    Deciduous, monoecious trees or shrubs. Bark grey, smooth. Buds fusiform or ovoid, acute at apex. Leaves alternate, with 9 or more pairs of veins, simple; stipules caducous. Flowers in unisexual catkins. Male catkins pendulous; one flower in the axil of each bract, without bracteoles; perianth absent; stamens about 10, with bifid filaments. Female catkins pendulous and spike-like, with 2 flowers in the axil of each bract; each bract accompanied by 6 bracteoles; flowers with the perianth small and irregularly lobed; ovary with 2 loculi; styles 2. Fruit a nut, subtended by a lobed or serrate, strongly veined involucre.

    Contains over 25 species in the north temperate regions and central America.

  • 30 - Nymphaeaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 129-132

  • Summary

    Perennial water or marsh plants usually with stout, creeping rhizomes. Leaves floating, submerged or aerial; floating leaves peltate or cordate, usually long-petioled; submerged leaves simple, thin and translucent. Flowers solitary, terminal, generally floating, bisexual, actinomorphic, hypogynous to epigynous, the parts variously arranged. Perianth usually differentiated into 3–6 green sepals and 3 to many petals which may pass gradually into the usually numerous stamens with introrse anthers and are either hypogynous or inserted at various heights on the wall of the more or less inferior ovary. Carpels 8 or more, either free, but then sunk in the receptacle, or united and superior or united into a many-celled ovary and inferior. Ovules 1–many, inserted over the inner walls of the carpels. Fruit a group of achenes sunk in the receptacle or a spongy capsule dehiscing regularly or irregularly by the swelling of internal mucilage; seeds often with arils, with or without endosperm, sometimes with perisperm as well as endosperm.

    Contains about 3 genera with some 75 species, cosmopolitan.

  • Flowers white, rarely red; ovary semi-inferior 1. Nymphaea

  • Flowers deep yellow; ovary superior 2. Nuphar

    • Nymphaea L. nom. conserv.

    Castalia Salisb.

    Perennial herbs with stout rhizomes. Leaves more or less subrotund, rarely peltate, with stipules. Flowers usually floating, often large and showy. Sepals (3–)4(–5), green, hypogynous. Petals numerous, inserted at successively higher levels on the side of the half-inferior ovary, the outermost much longer than the sepals, the innermost shorter and narrower and grading into the stamens. Stamens numerous, the outer with broad, petaloid filaments, all inserted towards the top of the ovary. Nectaries absent. Ovary syncarpous, many-celled with numerous ovules in each cell, concave above with a boss at the centre from which the stigmatic surfaces radiate. Fruit a spongy, berry-like capsule, splitting by the swelling of internal mucilage to release the seeds, which float because of the air-containing aril and seed wall.

  • 15 - Thelypteridaceae

  • from Division 3 - Polypodiophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 26-28

  • Summary

    Perennial herbs with a long and slender or short and thick rhizome with scales. Fronds borne singly or in dense terminal tufts, with sparse or very sparse scales, spirally coiled when young, of one or two kinds, almost 2-pinnate, with entire to crenate or sinuate pinnules. Sori in a row on underside of pinnule, usually near the margin. Indusia absent or small, thin and soon withering. Plants homosporous. Gametophyte green, surface-living.

  • 44 - Betulaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 333-355

  • Summary

    Leaves alternate, simple; stipules caducous. Male flowers in pendulous catkins, 3 together in a dichasium in the axil of each bract; bracteoles 2 to 4 to each group of flowers; perianth present. Female flowers in erect cylindrical or ovoid catkins, 2 or 3 together in a dichasium in the axil of each bract; bracteoles 2 to 4 to each group of flowers; perianth absent; ovary 2-celled; ovule one in each cell, anatropous, pendulous; styles 2, free. Fruit a flattened nut, single or in a group of 2 or 3 on the surface of a scale formed from the accrescent fused bract and bracteoles, in a dense cylindrical or cone-like strobilus; seed 1, endosperm absent.

    Contains 2 genera and about 95 species in north temperate regions and tropical mountains; central Andes.

  • Flowers opening with the leaves; stamens 2, bifid below the anthers; fruiting strobili cylindrical, with 3-lobed scales, falling with the nuts 1. Betula

  • Flowers opening before the leaves; stamens 4, entire; fruiting strobili cone-like, with 5-lobed persistent scales 2. Alnus

    • Betula L.

    Deciduous, monoecious trees and shrubs. Trunk slender and extending well into the crown. Bark smooth and resinous, marked by long longitudinal lenticels, often separating into thin papery plates, often becoming thick, deeply furrowed and scaly at the base of old trunks. Twigs roughened by crowded leaf-scars of many years; young shoots clothed with varying amounts of lenticels, or lenticels absent; simple eglandular hairs or peltate glands are often diagnostic. Buds with numerous scales, which are fully grown and bright green at midsummer. Leaves usually alternate, sometimes in pairs or threes on short shoots, sometimes incised-lobed; stipules scarious and usually caducous. Male and female flowers in 3-flowered dichasia, arranged spirally in separate catkins, with the lateral flowers of the dichasium subtended by bracteoles adnate to the base of the scale. Male catkins long and pendulous, solitary or clustered, appearing in summer or autumn in the axils of the last leaves of a young shoot and near the ends of short lateral twigs, erect and naked during the winter; scales in the spring broadly ovate, rounded, short-stalked, yellow or orange below the middle and dark chestnut-brown above; flowers with a membranous 4-lobed calyx, often 2-lobed by suppression, with the anterior lobe obovate, rounded at the apex, much longer than the minute posterior lobe; the 2 bifid stamens inserted at the base of the calyx.

  • 66 - Cucurbitaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 611-616

  • Summary

    Monoecious or dioecious annual or perennial herbs, often fleshy and bristly, usually with tendrils. Leaves alternate. Flowers unisexual, racemose, clustered or solitary. Calyx normally 5-lobed; rarely sepals free. Corolla normally 5-lobed, yellow or white. Stamens 5, often reduced to 3, two double and one single; anthers twisted or contorted. Ovary inferior; carpels united, usually 1–3 celled; placentation parietal. Stigmas as many as carpels. Fruit normally a fleshy, indehiscent berry, sometimes of considerable size; seeds usually numerous.

    Contains about 120 genera and 800 species, cosmopolitan but mainly in tropical and warm temperate areas.

  • The Cambridge school of plant taxonomy

  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp xv-xxv

  • Summary

    Much of what is in this flora is owed to the great historic background to plant taxonomy here in Cambridge. One cannot but feel that one is following in a great tradition when studying the British and Irish floras in the Cambridge University Herbarium, its Library and the University Botanic Garden and when using them to work out the results of one's fieldwork.

    When the modern western world took shape after the so-called Dark Ages it was France, Germany, Italy and the Low Countries that produced the pioneers of the science of botany. The medievalists were remote from any scientific appreciation of nature. An example of the work of a Cambridge scholar towards the end of that period is the book by John Maplet, A greene forest, or A naturall historie vvherein may bee seene first the most sufferaigne vertues in all the whole kinde of stones & mettals: next of plants, as of herbes, trees, shrubs, lastly of brute beastes, foules, fishes, creeping wormes serpents, published in 1567. It would be thought that by then the Renaissance and Reformation would have been established, but in thought this book is purely medieval. The breakdown of medieval ideas in England was to start at Oxford and then to be transferred to Cambridge, and it was the spirit of Erasmus in his writings, and above all in his edition of the New Testament, that gave an impetus to Greek studies and a new understanding of classical civilisation in the University.

    Two men at Cambridge, William Turner and John Caius, can properly be said to have started the long line of field naturalists in Britain. Both studied in Italy and both were friends of the great Zurich naturalist Conrad Gesner. Of the two, William Turner was by far the more important botanically, being one of the most vigorous of reformers and our first scientific student of botany and zoology.

    William Turner (1508–1568) was born at Morpeth in Northumberland and as a boy was said to notice the ways of animals and plants. In 1526 he went up to Pembroke Hall in Cambridge, where he stayed until 1537 and published a number of works. His teachings as a reformer got him into trouble and he went abroad, whether by order or his own choice is not known. He visited Belgium, Holland, Germany, Italy and Switzerland.

  • 3 - Isoetaceae

  • from Division 1 - Lycopodiophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 6-7

  • Summary

    Aquatic or terrestrial, perennial, heterosporous herbs. Stems 1, rarely 2 rings of meristematic cells producing secondary tissue, short and stout, dichotomously branched, the roots arising from the 2- or 3-lobed stem base. Leaves crowded in a dense rosette, subulate or filiform, usually more or less terete, often tubular and septate, sheathing at base; with a minute ligule on the upper side near the base. The first-produced leaves in any season bearing megasporangia, the next microsporangia, and the last sterile. Sporangia sessile, more or less embedded in the leafbase below the ligule and usually covered by an indusium formed from the leaf-base. Spores on germination giving rise to prothalli. Male gametophytes (from microspore) of one vegetative cell and an antheridium, with a 4-celled wall surrounding 2 cells which give rise to 4 spermatozoids. The multiciliate spermatozoids are liberated by the dehiscence of the spore and breaking down of the antheridium wall. Female gametophyte (from megaspore) is manycelled, fills the megaspore and bears archegonia, the necks of which protrude from the split top of the megaspore. The young plant develops with a resting stage from the fertilised archegonium.

    Contains 2 genera, Isoetes and the monotypic Stylites from the Andes of Peru, sometimes only recognised as a subgenus.

  • 65 - Frankeniaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 610-611

  • Summary

    Perennial herbs, often with woody bases, or small shrubs. Leaves opposite, without stipules, often ericoid. Flowers solitary, terminal or in the forks of the branchlets. Calyx somewhat fleshy; lobes 5, connate at base. Petals 4–6, clawed, with a scale-like appendage on the claw. Stamens usually 6, in 2 whorls of 3; anthers 2-celled, opening lengthwise. Style 1, divided into 3 near the apex; stigmas 3, elongate. Ovary superior, 1-celled, with 2–4 parietal placentae; ovules numerous. Fruit a capsule enclosed in the calyx, opening by valves; seeds endospermous; embryo straight and axile.

    Frankenia L.

    As family.

    Contains about 80 species with the distribution of the family.

  • 47 - Aizoaceae

  • from Division 5 - Magnoliophyta
  • Peter Sell, University of Cambridge, Gina Murrell, University of Cambridge
  • Book:
    Flora of Great Britain and Ireland
    Print publication:
    12 April 2018, pp 366-372

  • Summary

    Annuals or slightly to moderately woody perennials. Leaves opposite and often decussate or alternate, simple, usually entire, usually thick and succulent; petiole present or absent; stipules absent. Flowers solitary or in cymes, actinomorphic, usually bisexual, epigynous to perigynous. Hypanthium usually cup-shaped and persistent, often regarded as the tube of the calyx. Sepals 4–5(–6), joined to the rim of the hypanthium. Petals, actually petaloid staminodes, absent or numerous and more or less free and in one to several rows, usually linear and often brightly coloured. Stamens 3 to numerous, usually in several rows. Styles as many as carpels, free or fused at the base; stigmas minute or linear. Fruit a hooded, dehiscent or indehiscent capsule with 3 to many seeds or succulent with many seeds; loculi often roofed.

    About 130 genera with some 2500 species, widely distributed but common in South Africa.

  • 7 - Dinophyta

  • from Part IV - Evolution of One Membrane of Chloroplast Endoplasmic Reticulum
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 250-297

  • Summary

    These organisms are important members of the plankton in both fresh and marine waters, although a much greater variety of forms is found in marine members. Generally the Dinophyceae are less important in the colder polar waters than in warmer waters. The highly elaborate Dinophysales (Fig. 7.47(d), (e)) are essentially a tropical group.

    A typical motile dinoflagellate (Figs. 7.1, 7.2) consists of an epicone and hypocone divided by the transverse girdle or cingulum. The epicone and hypocone are normally divided into a number of thecal plates, the exact number and arrangement of which are characteristic of the particular genus (Figs. 7.1, 7.3, 7.20(b), 7.24(b)). There is a longitudinal sulcus running perpendicular to the girdle. The longitudinal and transverse flagella emerge through the thecal plates in the area where the girdle and sulcus meet. The longitudinal flagellum projects out from the cell, whereas the transverse flagellum is wave-like and is closely appressed to the girdle. The cells can be photosynthetic or colorless and heterotrophic. Photosynthetic organisms have chloroplasts surrounded by one membrane of chloroplast E.R., which is not continuous with the outer membrane of the nuclear envelope. Chlorophylls a and c 2 are present in the chloroplasts, with peridinin and neoperidinin being the main carotenoids. About half the Dinophyceae that have been examined by electron microscopy have pyrenoids in the chloroplasts (Dodge and Crawford, 1970). The storage product is starch, similar to the starch of higher plants (Vogel and Meeuse, 1968), which is found in the cytoplasm. An eyespot may be present. The nucleus has permanently condensed chromosomes and is called a dinokaryotic or mesokaryotic nucleus.

    Cell Structure

    Theca

    The thecal structure of motile Dinophyceae consists of an outer plasmalemma beneath which lies a single layer of flattened vesicles (Figs. 7.2, 7.3(c), 7.5) (Dodge and Crawford, 1970 ; Sekida et al., 2004). These vesicles, which normally contain cellulosic plates, give the theca its characteristic structure. The actual form and arrangement of the thecal plates varies from none in the phagotrophic Oxyrrhis marina, to very thick plates with flanges at the edges in Ceratium (Figs. 7.11, 7.48, 7.49) and Peridinium spp. (Figs. 7.2, 7.10).

  • Preface to the First Edition

  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp xiii-xiv

  • Summary

    It was that eccentric British soldier of fortune Col. Meinertzhagen, in his Birds of Arabia, who expressed the sentiment that prefaces should be kept short because few people ever read them. Accordingly, I would like to take a brief opportunity to express my gratitude to the people who offered encouragement and assistance during the preparation of this book. I would like to thank Adele Strauss Wolbarst, Robert Cnoops, Charmaine Slack, Sophia Skiordis, Caroline Mondel, Jill Keetley- Smith, Heather Edwards, Gail Arbeter, and the Lending Library at Boston Spa, England, for help while most of this manuscript was being prepared at the University of the Witwatersrand. For general encouragement while at Pahlavi (Shiraz) University and for providing assistance during the last turbulent and chaotic year of imperial rule in Iran, while the manuscript was being finished, I would like to thank Mark Gettner, Brian Coad, and Mumtaz Bokhari. When photographs or drawings have been taken directly from the original material, this is indicated by stating in the legend that it is from the original work. Most of the drawings have been redrawn to suit my tastes, and these drawings are indicated by stating that the work is after the original.

    In some cases I have made drawings from photographs or have incorporated a number of drawings in one, in which case I state that the finished drawing is adapted from the original work or works. I have used the metric system in this book, and the fine-structural illustrations are expressed in micrometers (μm) and nanometers (nm).

  • 12 - Heterokontophyta, Eustigmatophyceae

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 339-342

  • Summary

    Eustimatophytes are yellow-green unicells that occur in freshwater, brackish water, and seawater as well as in the soil. The cells are similar to those in the Xanthophyceae, but differ in having an eyespot outside the chloroplast (Fig. 12.1) (the eyespot in the Xanthophyceae is in the chloroplast) (Hibberd and Leedale, 1970). Other characteristics of the class include a basal swelling of the tinsel flagellum adjacent to the eyespot, only chlorophyll a, chloroplasts without girdle lamellae and no peripheral ring of DNA, and chloroplast endoplasmic reticulum not connected to the nuclear envelope (Schnepf et al., 1996).

    The eyespot (Figs. 12.1, 12.2) is a large orangered body at the anterior of the motile cell and is completely independent of the chloroplast. It consists of an irregular group of droplets with no membrane around the whole complex of droplets. The flagellar sheath is extended to form a T-shaped flagellar swelling at the base of the tinsel flagellum (Figs. 12.1, 12.2). This swelling is always closely appressed to the plasmalemma in the region of the eyespot. In turn, in the eyespot there is a large droplet closely applied to the plasmalemma in the area of the flagellar swelling.

    The chloroplasts of the Eustigmatophyceae have chlorophyll a and β-carotene, with the two major xanthophylls being violaxanthin and vaucheriaxanthin (Whittle and Casselton, 1969 ; Antia and Cheng, 1982), the only difference in pigments compared to the Xanthophyceae being the presence of violaxanthin and the absence of antheraxanthin. Violaxanthin is the major lightharvesting pigment in the Eustigmatophyceae (Owens et al., 1987).

    The Eustigmatophyceae is a monophyletic group (Andersen et al., 1998). Most of the species produce zoospores with only a single emergent flagellum (Pleurochloris magna, Fig. 12.1(d) ; Polyhedriella helvetica, Fig. 12.1(b))(Hibberd and Leedale, 1972), but there is a second basal body present, indicating that the cells had a biflagellate ancestor. The emergent flagellum is tinsel with microtubular hairs, and the flagellum is inserted subapically. Two of the algae in the class, Ellipsoidion acuminatum and Pseudocharaciopsis texensis (Fig. 12.2) (Lee and Bold, 1973), have zoospores with a long forward tinsel flagellum and a short posteriorly directed smooth flagellum.

  • 23 - Algae and the Environment

  • from Part V - Evolution of Two Membranes of Chloroplast Endoplasmic Reticulum and the Chlorarachniophyta
  • Robert Edward Lee, Colorado State University
  • Book:
    Phycology
    Published online:
    06 August 2018
    Print publication:
    01 March 2018, pp 492-509

  • Summary

    It is possible to write whole books on the relationships between algae and the environment. In this chapter I have chosen a few subjects that have generated the most interest in the past couple of decades.

    Toxic Algae

    Algae can be harmful in two basic ways (Hallegraeff et al., 2003 ; Lassus et al., 2016).

    (1) Producing large populations in the aquatic environment. Large growths of some algae (e.g., the diatom Chaetoceros (Figs. 17.36, 17.37(a)) or the prymnesiophyte Chrysochromulina (Fig. 23.1(c))) can clog the gills of fish and can be particularly a problem in aquaculture systems. Anoxic conditions, resulting in fish kills, can occur at the end of blooms of other algae (e.g., green algae) as the algae die and decompose.

    (2) Production of toxins Some algae produce toxins that sicken and kill other organisms that prey on these algae. Indeed, this probably was the reason that these algae were selected for in the evolutionary process since it reduced predation by grazers (Gilbert, 1996). Filter-feeding shellfish can accumulate large quantities of these toxins as they filter the algae out of the water (Rossini and Hess, 2010). Consumption of the shellfish by man, birds, and animals results in sickness and death. The algae that produce phycotoxins are as follows.

    Cyanophyceae (cyanobacteria)

    • Neurotoxins anatoxin (Fig. 23.2(c)) and saxitoxin (Fig. 23.2(c)) that block the transmission of signal from neuron to neuron. These alkaloids (nitrogen-containing compounds) bind to voltage-activated Na + - channels and block influx of Na +, thereby preventing the generation of an action potential (Shimizu, 2000).

Page 36 of 589