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Transcript
53 Botanical Lessons Plant organisation (1/2) Leaves of the family Crassulaceae (here the example of the houseleek, Sempervivum montanum) can store water as an adaptation to drought Flowering plants are composed of three parts: roots, stems and leaves. Potatoes are stems that have been modified to store nutrient reserves. In common with all stems, they carry the buds ("eyes") blade veins Roots. Most often found underground, roots anchor plants to the soil and absorb water and mineral elements required for growth. They can be either taproots (a single vertical root) or fasciculate. Sometimes roots also store reserves (such as in the carrot). The stem. Generally found aboveground, stems carry the buds, which determine the growth, ramification and flowering of the plant. Stems maintain the plant upright and are essential for the petiole stipules alternate opposite General organisation of a leaf and examples of the arrangements "alternate" and "opposite" transport of nutrients (sap). Stems can be herbaceous, or rigid and lignified (wood) in shrubs and trees. Diagram of a plant: roots (in black, here fasciculate, with numerous roots attached to the same point), stem (in brown), leaves (in green) and a flower (in blue). The stolons are above ground stems which grow horizontally and produce clones of the mother plant. Leaves. Leaves are the principal organ of photosynthesis and transpiration. They generally comprise of two parts: the lamina and the petiole. The lamina is a flattened blade containing veins lanceolate ovate obovate orbicular sagittate pennatilobate cordate which transport the sap. The shape, margin and pattern of veins differ between species and constitute criteria for identification. The lamina is divided into leaflets, in the case of leaves called pedate “compound” leaves. The petiole, which is sometimes absent, attaches the leaf to the stem. Phyllotaxy describes the arrangement of leaves on the stem. Leaves can, for example, be grouped An example of a plant with both an underground stem, or rhizome (in brown), and an above ground stem; the roots (in black) are called “adventive” (newly formed on the stem) in pairs attached face to face along the stem (leaves called "opposite") or be rather isolated and arranged regularly in a spiral around the stem (leaves called "alternate"). palmate paripennate imparipennate A few examples of the diversity of leaf blades. In brown, the petiole, in dark green, some examples of "compound" leaves Botanical Lessons 53 Plant organisation (2/2) Two gentians: Gentianella campestris (left, hemicryptophyte) and Gentiana nivalis (right, a rare alpine therophyte) The daffodil (Narcissus poeticus, Amaryllidaceae family), an example of a cryptophyte plant with a bulb The Danish botanist Christen Raunkiær (1860-1938) developed a classification of plants founded on their strategies to survive bad winter conditions. This classification is based on the position of plant A. Phanerophytes (trees, shrubs > 50 cm) Perennial plants Annual plants B. Chamephytes subshrubs (a), creeping shrubs (b), plants with woody basee (c) C. Hemicryptophytes rosettes (d ), tufts (e) D. Cryptophytes (ou geophytes) with rhizome (f ), or bulb (g) buds during the winter. Phanerophytes are trees and shrubs higher than 50 cm. Their buds are not protected from frost by snow cover, which is one of the reasons that trees are absent from the alpine zone. Chamephytes are small shrubs whose buds are sufficiently low to be protected by snow cover. Numerous cushion plants from dry mountain areas (see the rockery “Spanish mountains”) have E. Therophytes woody bases and also belong to this category. Hemicryptophytes have their buds located at soil A C level, and their leaves form either a rosette (such as the Dandelion) or a tussock (such as in numerous D e Poaceae or Cyperaceae). Cryptophytes (also called Geophytes) have their buds buried, and thus f B 50 cm a c d g E b protected from cold under the ground (geo in Greek). The buds are situated on the rhizomes (underground stems) or on bulbs which accumulate reserves to fuel the beginning of growth for the next year. Therophytes are annual species. These species pass the winter period as seeds, highly resistant to aridity and frost. Very common in arid areas, annual species are almost non-existent in alpine areas, mostly because of the highly random nature of the possibility for sexual reproduction at high altitudes. The principal "biological types" based on the position of the buds during winter (in red). In black, the perennial parts of the plant that remain from one year to the next; dotted lines, the plant parts that die during the winter. Etymology of the terms: "phanero", visible; "chamae", dwarf; "hemi", half; "crypto", hidden; "thero", summer. Botanical Lessons 53 The concept of the alpine plant (1/2) The mountain avens (Dryas octopetala, Rosaceae family), an example of an arctic-alpine plant The gentians (here Gentiana acaulis, Gentianaceae family), examples of plants originating from the Himalayan region Altitudinal vegetation zones. Mountain vegetation is divided into zones, each with a characteristic type of vegetation. The upper limit of the sub alpine zone marks the natural limit (without human South ADRET North 2400 m zone where environmental conditions become more and more extreme with altitude due to decreasing mean temperatures, increasing solar radiation, strong winds, etc. The sub alpine / alpine NIVAL belt 3000 m intervention) of trees. This limit is found around 2300 m altitude in the Alps. Higher up is found the alpine UBAC mosses, lichens 2900 m ALPINE belt come from subalpine and alpine zones. Etage SUBALPIN conifer forests Multiple origins for the flora of the Alps. The current alpine flora is the result of a colonisation begun some 10 000 years after the retreat of the glaciers. The major vegetation influences come from the MOUNTAIN belt mixed forests COLLINEAN belt broadleaved forests Routes of the plant colonisation of the Alps: 1, Mediterranean; 2, Central Asian; 3, Arctic endangering those plants that grow at high altitudes. The plants growing in the Lautaret alpine garden 1500 m 1100 m an alpine plant is a species that grows in the alpine zone, in the Alps or another mountain region. Determined mostly by temperature, the limit of the alpine zone is rising due to global warming, alpine meadows 2200 m 1700 m boundary varies from 0 m altitude in polar areas, up to above 4000 m in tropical regions. For biologists, 900 m Mediterranean, Central Asian (notably Himalayan) and arctic regions. In the case of the arctic region, the alternation between glaciations and glacial retreat has contributed to numerous exchanges of flora, resulting in the presence of numerous plant species, called arctic-alpine species, which are found both in the Alps and in arctic regions. The campanulas (here Campanula alpestris, Campanulaceae family), a plant with a Mediterranean origin Botanical Lessons 53 The concept of the alpine plant (2/2) Swiss androsace (Androsace helvetica, Primulaceae family), a cushion plant growing amongst rocks at the Galibier pass (around 2800 m) High altitude Dwarf willow (Salix serpyllifolia, Salicaceae family) an example of a prostrate plant Morphological adaptations. A small size is very common amongst alpine plants, allowing them to at the surface of the cushion Temperature(°C) 25 remain within 1 to 2 m of the ground where temperatures are less cold. It also allows plants to benefit 20 from protection by snow cover in winter, and limits the mechanical effects of the wind and snow which 15 10 can break stems and branches. Cushion plants are a well-known example of adaptation to extreme at 2 m from the cushion 5 conditions: the cushion functions as a heat trap as its geometric form exposes the least surface area to 0 9 external conditions, limiting both losses of heat (and water). Plant hairs are another adaptation: these 12 15 18 Hour of the day (summer) form a screen that protects the plant from cold, dry and strong solar radiation. Root systems of alpine The temperature difference between the surface of a cushion plant and at two meters height (using the example of silene acaule) Vitamin C, micromol/mg chlorophylll Structure of the Swiss androsace, an example of a cushion plant with a long tap root Physiological adaptations. Alpine plants synthesise molecules (sugars, anti-freeze proteins) which alpine plants protect their cell membranes from the effects of freezing. They can also maintain their cell contents in 5 4 a liquid state down to temperatures of -40°C. To counter oxidative stress imposed by excessive solar 3 lowland plants 2 radiation (light and UV), plant can accumulate anti-oxidants, in particular vitamin C. These adaptations are the results of long periods of evolution. They are in part fixed in the genetic makeup of 1 0 plants can also exhibit adaptations, such as the presence of a long tap root in cushion plants. 1 2 3 4 5 6 Differences in the concentration of vitamin C in three alpine plants (1, soldanella; 2, alpine coltsfoot; 3, glacier ranunculus) and three lowland plants (1, rye; 2, dandelion; 3, meadow buttercup) alpine species, and in part dependant on environmental conditions (acclimation). Ces adaptations sont le fruit d'une longue évolution. Elles sont pour partie inscrites dans le patrimoine génétique des espèces et pour partie conditionnées par les conditions environnementales (acclimatation). The edelweiss (Leontopodium alpinum, Asteraceae family), an example of a plant covered with protective hairs Botanical Lessons 53 Interspecific relationships (1/2) Mont Cenis restharrow (Ononis cenisia, Fabaceae family), an example of a plant able to fix atmospheric nitrogen Lousewort (Pedicularis comosa, Orobanchaceae family), an example of a hemiparasitic plant Plants have multiple types of relationships between each other, and with other organisms atmospheric nitrogen (N2) (bacteria, animals). Here are a few examples Symbiosis. This is a long term association between two organisms allowing each to obtain organic nitrogen (proteins) root nodules (Rhizobium bacteria) Diagram of the symbiosis between the Fabaceae (Leguminaceae) and the bacteria hosted in the nodules of their roots reciprocal advantages. Plants such as the sainfoins, trefoils, milk-vetches, restharrows, clovers and other plants of the family Fabacea, host in their roots (within nodules) bacteria (Rhizobium) which roots of the parasite (haustorium) can use atmospheric nitrogen. They transform this into organic nitrogen (amino acids and proteins) water and mineral nutrients which can then be used by the plant. Similarly, lichens are the result of a symbiosis between a fungus, which provides resistance to drying out, and an algae, which provides the synthesis of host roots Hemiparasitism sugars by photosynthesis. CO2 (atmospheric carbon) sugars (organic carbon) O2 fungal mycelia unicellular algae Diagram of lichen with the fungal mycelium (in brown) and the unicellular algae (in green) Parasitism. This is a relationship with negative consequences for one organism. In the case of hemiparasitism (louseworts, rhinanthus, velvetbells, etc.), one plant accesses water and mineral salts in the vessels (roots or stems) of the host plant, but remains green and able to also photosynthesise itself. In the case of holoparasitism (such as for the broomrapes and dodder), the parasite has lost the capacity to photosynthesise itself, and not only uses water and mineral salts from the host, but also organic matter. roots of the parasite (haustorium) water and mineral nutrients + organic matter host roots Holoparasitism 53 butterwort leaf enzymes (proteases) insect Botanical Lessons Interspecific relationships (2/2) Facilitation: lady's mantle (Alchemilla sp) (dissected leaves) benefits from the favourable microclimate next to a cushion of moss campion (Silene acaulis) Competition between Festuca paniculata (large grasses) and other species in grasslands at the Col du Lautaret Carnivory. Carnivorous plants live in wet, poorly oxygenated areas which are low in nitrogen, which is required for the synthesis of amino acids and proteins. The solution found by these plants consists of trapping insects within their leaves (Butterworts and Droseras have sticky leaves) which are then digested by enzymes produced by the leaves. The amino acids that are liberated are then absorbed by the leaves and are used in the synthesis of proteins by the plant. organic nitrogen (amino acids) An insect digested by the sticky leaves of the butterwort Pinguicula vulgaris (Lentibulariaceae family) Competition and facilitation. these are relationships which are not essential to the survival of one of the partners such as in the case of parasitism or symbiosis. These types of relationships affect the growth of plants either negatively (competition) or positively (facilitation). In the case of competition, plants compete for light Competition Facilitation No interaction the plant grows less well with neighbours the plant grows better with neighbours the plant grows in the same manner with or without neighbours and mineral nutrients, which reduces the growth of less competitive species. In the case of facilitation, one plant benefits from the environment created by another plant which favourably modifies the microclimate (protection from cold, aridity, excessive solar radiation, etc.). Plant with neighbouring vegetation Plant without neighbouring vegetation (Neighbour removal) Diagram showing three types of interactions that can exist between plant species: when plants neighbours are experimentally removed, the plant can either grow better, less well, or in the same manner, which indicates the types of interactions that are occurring between the plant and its neighbours Botanical Lessons 53 Plant distributions (1/2) Saxifraga bryoides (mossy saxifrage), grows only amongst acid siliceous rocks of the Alps and some other European mountain areas Saxifraga caesia (Mount Cenis saxifrage), grows only amongst alkaline limestone rocks of the Alps and some other European mountain areas Some aspects of the distribution of alpine plants are presented here using the example of the genus Saxifraga (Saxifragaceae family). This genus comprises of more than 400 species, essentially found in the mountains of the temperate and arctic northern hemisphere, with many species found in the Alps. Some species, called arctic-alpine, such as Saxifraga oppositifolia or S. aizoides, have a broad distribution in the arctic region, in the Alps and other European mountains (1). Initially distributed in the arctic, these species migrated towards the south during the period of glaciation. As the glaciers 1. Distribution of Saxifraga oppositifolia in Europe, an arctic –alpine species. During the glacial period, it grew in rocky ice free areas retreated, these species recolonized the arctic as well as the higher areas of the Alps. 2. The distribution of the two species Saxifraga caesia and Saxifraga bryoides, two plants found in the Alps and in other mountain regions Other species are not present in the arctic region. Saxifraga caesia and S. bryoides (2) are two species with a broad distribution in the Alps and some other mountain massifs. Despite their similar distribution, the two species are not found together as they have different requirements as to the type of areas they grow in, one grows in limestone areas (S. caesia) and the other on silicates (S. bryoides). This is called ecological vicariance. Other species such as Saxifraga biflora only grow in the Alps (endemic species, 3). However, it should be noted that this species also grows on a mountain in Saxifraga oppositifolia, pink flowers) Saxifraga biflora, white flowers) and Greece, maybe transported by birds, or maybe as an indicator that previously the species had a much larger distribution (relictual species).temps où l'espèce avait une distribution plus large. 3. The distribution of Saxifraga biflora, a species which grows only in the Alps (and on Mount Olympus in Greece) 53 Botanical Lessons S. hostii S. valdensis Plant distributions (2/2) S. cochlearis Saxifraga valdensis, a protected species that grows in France only in a few locations in the Queyras massif Distribution of Saxifraga valdensis (westernAlps), S. hostii (eastern Alps) et S. cochlearis (ssouthern Alps) The species presented here correspond to three species whose ecological requirements are similar (plants growing in alpine zone rocky areas), but they are found in distinct geographical areas: the eastern Alps in the case of S. hostii; the Maritime Alps for S. cochlearis and the western Alps between France and Italy for S. valdensis. This is a case of geographical vicariance. In the case of the species shown opposite, scientific research has allowed for an understanding of how these distributions developed. These species (as well as others not shown on the map) are all descended form an ancestral species, Saxifraga cespitosa, which is still found today in arctic regions. During the glacial period, this species migrated towards the south. With the retreat of the glaciers, this species recolonized the arctic areas and also most of the mountains of southern Europe. Within each of these mountain regions, geographical isolation allowed for the divergent evolution of this original species, and for the development of a series of endemic species. A number of these endemic species can be found in this rockery, in the Pyrenees rockery (S. hariotii) or in the "Massif central" rockery (S. cebennensis). Botanical Lessons 53 Sexual reproduction Flowers of the vernalgrass (Anthoxanthum odoratum, Poaceae family), an example of a plant pollinated by the wind Two insect pollinated plants with very colourful flowers (Peacock-eye pink and the common rock-rose) The flower is the central element of sexual reproduction in plants. The flower is the central element of petal sexual reproduction in plants. It comprises of the fertile parts: stamens (male organs) and carpel (female organs), and the sterile parts: petals and sepals. The majority of flowers are hermaphrodites, having both anther filet stamen sepal style ovary ovule pistil male and female organs. They can be isolated, or grouped in inflorescences. The stamens are formed of an axis (stalk) supporting at its extremity an anther, often yellow, which contains the pollen grains. The carpel consists of an ovary containing the ovules, and one or more styles that end in a stigma, which peduncle The different parts of a flower, shown here for the alpine flax (Linum alpinum, Linaceae family) receives the pollen. Pollen is transported by different vectors. Most often, it is insects that transport pollen, spike capitulum corymb raceme umbel and in this case the evolution of flowers has resulted in the development of attractive features such as bright colours, scents, particular forms or sugary nectars. In other cases, it is the wind that transports pollen, and the flowers have no petals and no colour (for example in the Poaceae or the Cyperaceae). Once on the stigma, a pollen grain will fertilise an ovule, which will ultimately become a seed, within a pistil that transforms into a fruit. The fruit aids in the dispersal of the seed by the wind, by animals, by water, etc. At high altitude, flowers often have intense colours or flower for longer, to compensate for the rarity of insect pollinators. Many species also reproduce asexually (clonally) or through apomixis (the An example of a compound umbel, typical of the Apiaceae family (Umbelliferae), shown here for the common hogweed (Heracleum sphondylium) production of seeds and fruits without fertilisation, such as found in the Hawkweeeds. panicle composed umbel thyrse The principal types of inflorescences (location of flowers on a stem). The arrows indicate the progression of flowering of the flowers shown in red 53 Botanical Lessons Clonal reproduction (asexual) The stolons of the creeping avens (Geum reptans, Rosaceae) allow the plant to colonise schist scree slopes Clonal reproduction allows the violet fescue (Festuca violacea, Poaceae) to form mats which stabilise the slope Asexual reproduction, which is also called vegetative or clonal reproduction, generates exact copies of the original individual called clones. Asexual reproduction is a more reliable form of reproduction than sexual reproduction as it is independent of the season, of successful pollinisation and of seed dispersal. However, this mode of reproduction does not increase genetic diversity, which limits the evolution of species and their adaptation to changes in their environment. Alpine plants often utilize both types of reproduction, increasing their chances of reproduction in difficult environments. Numerous shrubs reproduce asexually by layering, in which buds located on branches lying on the Diagram showing the production, starting with a mother plant (left), of successive clones from a horizontal stem (stolon or rhizome) The foxtail grass (Alopecurus gerardi, Poaceae) has rhizomes which produce clones of the mother plant at their extremities ground begin to develop their own roots (such as in Rhododendrons and the Green Alder). In other species, plants can produce spreading aboveground stems called stolons (such as for Geums), or underground stems called rhizomes, which do not have green leaves and whose buds can produce clones (such as in numerous Poaceae, e.g. Alopecurus gerardi) Some plants produce bulbs, which are fleshy buds which detach from the base of leaves and produce clones of the mother plant (such as in the alpine bistort, and the orange lily). It is estimated that for some plants such as Carex curvula, the dwarf willow and the alpenrose, the same Sexual reproduction (flowers) in the alpenrose (Rhododendron ferrugineum, Ericaceae) which also uses clonal reproduction via layering clone can be aged numerous hundreds, or even thousands of years old. Flowers (sexual reproduction) and bulbs (clonal reproduction) in the orange lily (Lilium bulbiferum var bulbiferum, Liliaceae) 53 Botanical Lessons Systematics and classification (1/2) A drawing of a peony from the book "Éléments de botanique, ou méthode pour connaître les plantes" published by Tournefort in 1694 Berardia subacaulis Vill., a species described and named by the botanist from the Dauphine region, Dominique Villars, in 1789 Systematics is that part of botany that aims to classify plants into group’s best reflecting their similarities and differences. The criteria on which this classification is based are morphological characteristics ANCESTRAL GROUPS (structure of the flowers and vegetative parts), and more recently cytological characters (cell contents MONOCOTYLEDONS Commelinales Poales Asparagales Liliales Dioscorales The Greek philosopher Theophrastus (370-285 BC) developed the first plant classification for 480 plants Alismatales Ranunculales depending on their size (tree, shrub, or herb) and certain floral characteristics. The French botanist de Buxales Tournefort (1656-1708) established a classification of plants according to the structure of their flowers and Fagales Rosales Fabales Oxalidales the first corresponds to the genus and the second to the species, followed by the name of the author who first described it. The species are grouped into genera and then into families. For example, the belier peony DICOTYLEDONS things, called binomial, which is still used today. Each species is identified by two Latin (or Greek) names: Malvales Brassicales Sapindales Geraniales Saxifragales Caryophyllales Ericales illustrated opposite is the species arietina, within the genus Paeonia (peony), which belongs to the family Gentianales Lamiales Salanales Boraginaceae Paeoniaceae. Asterales Dipsacales AToday, the comparison of DNA sequences allows the further refinement of classifications based on centuries of methodical observations, and the adoption of a phylogenetic approach providing Plant labels from the garden using the nomenclature created by Carl von Linnaeus Magnoliales Laurales and structure) and genetics (DNA sequences). fruits. It was the Swedish naturalist Carl von Linnaeus who developed a universal nomenclature of living Carl von Linnaeus (1707-1778) Amborellales Nymphaeales Piperales information on the evolutionary history of different species and their evolutionary relationships. Apiales The phylogeny of flowering plants derived from the comparison of DNA sequences. The links represent evolutionary relationships. The names shown on the right are the "orders" which regroup several families. For example the "Ranunculales" contain the families Ranunculaceae and Papaveraceae 53 Botanical Lessons Systematics and classification (2/2) Alpine Columbine (Aquilegia alpina), a nationally rare and protected species. Note the hooked nectar spurs Meadow-rue (Thalictrum aquilegifolium), with its white flowers with numerous stamens. To the right, the yellow globeflower (Trollius europaeus) Identification key of the principal genera of the Rannunculaceae family present in the Alps For each plant in the rockery, choose between the two alternatives at level 1, and then continue similarly for each choice until arriving at one of the 12 genera (Clematis, Delphinium, Aconitum, etc.). In the case of the genus Aconitum, identify the three alpine species. You can verify your identifications using the plant labels Diagram of the structure of a flower: sepals in green, petals in white, stamens in yellow, fruits (achenes) in dark green 1. Leaves opposite, climbing plant 1. Leaves alternate, non-climbing plants 2. Flowers irregular, with only one plane of symmetry (zygomorphic) 2. Flowers regular, with multiple planes of symmetry (actinomorphic) 3. Flowers with a nectar spur 3. Flowers without nectar spurs 4. Flowers forming a yellow ball (the stamens and pistil are not visible 4. Flowers open (the stamens and pistil are visible) 5. Flowers with 5 hooked nectar spurs 5. Flowers without nectar spurs 6. Flowers with small green sepals and small hooked petals 6. Non matching characteristics 7. Flowers with petals and sepals both present and distinct 7. Flowers with only one type of sterile part (sepals), or completely without petals and sepals 8. Three sepals, flowers purple, blue or white 8. Five sepals, flowers yellow or white 9. Large sepals, resembling petals and very visible and strongly coloured 9. Four small sepals that fall very early, coloured stamens, highly dissected compound leaves 10. Five yellow-orange sepals, kidney shaped leaves 10. More than 5 white, purple or pale yellow sepals, very dissected leaves 11. Fruits (achenes) with a long feathery style ; Plants often covered with long hairs 11. Fruits (achenes) with deciduous style. Plants generally with few hairs CLEMATIS 2 3 4 DELPHINIUM ACONITUM see below TROLLIUS 5 AQUILEGIA 6 HELLEBORUS 7 8 9 HEPATICA RANUNCULUS 10 THALICTRUM CALTHA 11 PULSATILLA ANEMONE Wolfsbane (Aconitum lycoctonum), an extremely toxic species A key to some alpine species of the genus Aconitum, all highly toxic species Kupher’s ranunculus (Ranunculus kupferi), a species from wet alpine grasslands 1. Flowers yellow 1. Flowers blue 2. Narrow helmet, much taller than wide. Leaves with large lobes 2. Helmet only just taller than wide. Leaves with filliform lobes 2 Aconitum napellus Aconitum lycoctonum Aconitum anthora Alpine anemone (Pulsatilla alpina): the fruits (achenes) have a long feather-like style which grows after fertilisation