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The Temple of Flora Exploring the Biology of Plants 2 What is a plant? According to the Oxford English Dictionary a Plant is “A member of the lower of the two series of organized living beings i.e. of the vegetable kingdom; a vegetable; generally distinguished from an animal by the absence of locomotion and of special organs of sensation and digestion, and by the power of feeding wholly upon inorganic substances”. Spermatophyta (Seed Plants) • Seed plants are divided into two groups: • Gymnosperms • Angiosperms • Angiosperms are also divided into two groups: • Dicotyledons • Monocotyledons Gymnosperms • ‘Flowers’ are cones, with separate male and female cones (or, in some instances, plants). • Water-transporting veins composed of tracheids not vessels (more about this next week). • Well-known plants include cycads, spruces, pines, junipers, cypresses, maidenhair tree. Cycas circinalis Picea abies Pinus sylvestris Gingko biloba (and Adiantum capillus-veneris) Angiosperms • Flowering plants • Dicotyledons have two leaves in each seed – these constitute the bulk of the many tens of thousands of species. • Monocotyledons have only one leaf in each seed – such groups as grasses, orchids, bulbs (eg lily family, daffodil family), palms. Classification • • • • • • • Kingdom PLANTAE Division Spermatophyta Class Magnoliopsida Order Ranunculales Family Ranunculaceae Genus Ranunculus Species Ranunuculus acris Classification • The level (above genus and species) at which botanists work seems to depend on the group on which they are working. • Flowering Plant botanists most commonly work at the Family level. • Algal botanists (phycologists) tend to work at order, rather than family (or even, on a broader scale, at Class level). Rhododendron griersonianum Rosa ‘Red Chateau’ Pelargonium peltatum Disa uniflora Haemanthus multiflorus Crocosmia crocosmiiflora Meconopsis cambrica Rudbeckia Calendula officinalis ‘Neon’ Ranunculus acris Paeonia lutea ludlowii Narcissus Dendrobium densiflorum Euphorbia cyparissias Alchemilla mollis Acer pseudoplatanus Primula bhutanica Lactuca perennis Cichorium intybus Myosotis arvensis Delphinium elatum Saintpaulia Viola canina Echinacea purpurea Iris spuria ‘Lucky Devil’ Ornithogalum umbellatum Anemone japonica Campanula latifolia Geranium phaeum ‘Samabor’ Some thoughts on names • • • • • • • • • • Fuchsia magellanica Rhododendron forrestii Campanula latifolia Fucus vesiculosus Meconopsis betonicifolia Nepenthes alata Epilobium montanum Ammophila arenaria Lithothamnium glaciale Primula bhutanica What are flowers for? • ‘Flowers are created for the protection of the seed; they spread over it and cover it. Some of them protect it either against damage by wind, so mostly in fruit trees, or against damage by water in watery plants, such as the bugloss.’[1] • [1] Barhebraeus Butyrum VI, 3.2.4. (Nicolaus Damascenus – De Plantis – Five Translations edited and introduced by Drossaart Lulofs and Poortman. Amsterdam: North Holland Publishing Company. (1989: 100)). Who IS this man? • Nicolaus of Damascus was born in Damascus, c. 64 B.C., the son of wealthy parents probably of Macedonian origin and received an expensive liberal education. He became such a distinguished scholar that he came to the attention of Herod the Great, King of Judaea, and spent his life in the service of Herod and of his son Archelaus. It is not known what happened to him after the latter’s death. Why are flowers coloured? • ‘Colours then and shapes of plants are developed by the vegetative soul which underlies each of the mixed causes without being sentient, so that they become fair and comely – comparable to the natural power in the liver, the kidneys and in other parts of animals, which attracts the suitable, forces out the residue, makes the food similar to what feeds itself, and performs other amazing and marvellous actions, though it is not sentient.’[1] • [1] Barhebraeus Butyrum VI, 4.2.1. (Nicolaus Damascenus – De Plantis – Five Translations edited and introduced by Drossaart Lulofs and Poortman. Amsterdam: North Holland Publishing Company. (1989: 108)). Three separate processes • Pollination • Fertilisation • Seed Dispersal • Students frequently (one might almost say invariably) confuse these – particularly the first and the last. Reproduction in plants • ‘If a reader calls a body male that by nature has a capacity for moving a matter to receive a form similar to its own, and female a body that has a passive capacity for receiving a form in the above mentioned way, then plants have male and female, and it is possible that a single plant is male and female at the same time: female because the said matter is generated in it, and male because the said moving capacity originates in it.’[1] • [1] Barhebraeus Butyrum VI, 1.3.1. (Nicolaus Damascenus – De Plantis – Five Translations edited and introduced by Drossaart Lulofs and Poortman. Amsterdam: North Holland Publishing Company. (1989: 74)). Pollination • Movement of pollen from where it is produced (the anther) to the stigma (female receptive part of the flower). Period (as they would say on the other side of the Atlantic). • Plants may be self-pollinated (in which case pollen lands on a flower of the same plant (or same flower) or cross-pollinated (where two separate individuals are involved). Cross Pollination • Ensures genetic variability. • In many species there are mechanisms to ensure that only cross pollination can take place. Heterostyly in Primula i.e. Pin- and Thrum- Flowers Heterostyly in Primula i.e. Pin- and Thrum- Flowers Male/Female ripen at different times, as in Arum maculatum Pollination • A whole host of vectors are used in the different species to transport pollen – wind, water, insects (quite often specific groups or species), slugs, birds, small mammals (bats, tree-shrews, for example) to give just a few examples. • Plants have evolved in parallel with their pollinator, and floral morphology is very dependent on this. Abiotic pollination These do not attract animal pollinators. • Wind pollination (anemophily) • Flowers may be small and inconspicuous, as well as green and not showy. They produce enormous numbers of relatively small pollen grains (hence wind-pollinated plants may be allergens, but seldom are animal-pollinated plants allergenic). Their stigmas may be large and feathery to catch the pollen grains. Insects may visit them to collect pollen; in some cases, these are ineffective pollinators and exert little natural selection on the flowers, but there are also examples of ambophilous flowers which are both wind and insect pollinated. Anemophilous, or wind pollinated flowers, are usually small and inconspicuous, and do not possess a scent or produce nectar. The anthers may produce a large number of pollen grains, while the stamens are generally long and protrude out of flower. Anemophilous flowers Wind Pollination • ‘When over the heart of a palm tree something from the flower of a male is sprinkled, it ripens the fruit and prevents its falling off. The males in all trees are more dense and branching, harder and less fat; their fruits are small and do not ripen; with the females, however, it is the other way round. Many times, when the wind is strong, it carries the power of the male to the female.’[1] • [1] Barhebraeus Candelabrum II, 3.3.2. (Nicolaus Damascenus – De Plantis – Five Translations edited and introduced by Drossaart Lulofs and Poortman. Amsterdam: North Holland Publishing Company. (1989: 62)). Coconut Palm Abiotic pollination These do not attract animal pollinators. • Water pollination (hydrophily) • Water-pollinated plants are aquatic and pollen is released into the water. Water currents therefore act as a pollen vector in a similar way to wind currents. Their flowers tend to be small and inconspicuous with lots of pollen grains and large, feathery stigmas to catch the pollen. However, this is relatively uncommon (only 2% of pollination is Hydrophily) and most aquatic plants are insect-pollinated, with flowers that emerge into the air. Biotic pollination syndromes • A whole host of different animal groups pollinate flowers. • Although there are different terms for each group of insects, the general term for insectpollination is Entomophily. Bee pollination (melittophily) • Bee-pollinated flowers can be very variable in their size, shape and colouration. They can be open and bowl-shaped (radially symmetrical) or more complex and non-radially symmetric ("zygomorphic") such as many peas, foxgloves, etc. • Some bee flowers tend to be yellow or blue, often with ultraviolet nectar guides and scent. Nectar, pollen, or both are offered as rewards in varying amounts. The sugar in the nectar tends to be sucrose-dominated. • There are diverse types of bees, however. Honeybees, bumblebees, orchid bees, etc. are large groups that are quite distinctive in size, tongue length and behaviour (some solitary, some colonial). Thus generalization about bees is difficult. Some plants can only be pollinated by bees because their anthers release pollen internally, and it must be shaken out by buzz pollination (also known as "sonication"). Bees are the only animals that perform this behaviour. Bumblebees sonicate, but honeybees do not. • Bee pollination from mobile beehives is of great economic value for orchards such as apple or almond Actinomorphic and Zygomorphic Flowers Nectar Guides Nectar Guides Nectar Guides 3 Ophrys apifera Butterfly pollination (psychophily) • Butterfly-pollinated flowers tend to be large and showy, pink or lavender in colour, frequently have a landing area, and are usually scented. Since butterflies do not digest pollen (with one exception), more nectar is offered than pollen. The flowers have simple nectar guides with the nectaries usually hidden in narrow tubes or spurs, reached by the long tongue of the butterflies. Platanthera bifolia Moth pollination (phalaenophily) • Among the more important moth pollinators are the hawk moths (Sphingidae). Their behaviour is similar to hummingbirds: they hover in front of flowers with rapid wingbeats. Most are nocturnal or crepuscular. So mothpollinated flowers tend to be white, night-opening, large and showy with tubular corollas and a strong, sweet scent produced in the evening, night or early morning. A lot of nectar is produced to fuel the high metabolic rates needed to power their flight. • Other moths (Noctuids, Geometrids, Pyralids, for example) fly slowly and settle on the flower. They do not require as much nectar as the fast-flying hawk moths, and the flowers tend to be small (though they may be aggregated in heads). Night-scented stock Fly pollination (myophily and sapromyophily) • Flies tend to be important pollinators in high-altitude and high-latitude systems, where they are numerous and other insect groups may be lacking. There are two main types of fly pollination: myophily and sapromyophily. • Myophily includes flies that feed on nectar and pollen as adults particularly bee flies (Bombyliidae), hoverflies (Syrphidae), and others and these regularly visit flowers. In contrast, male fruit flies (Tephritidae) are enticed by specific floral attractants emitted by some wild orchids which do not produce nectar. Chemicals emitted by the orchid act as the fly's sex pheromone precursor or booster. Myophilous plants tend not to emit a strong scent, are typically purple, violet, blue, and white, and have open dishes or tubes. • Sapromyophiles, on the other hand, normally visit dead animals or dung. They are attracted to flowers which mimic the odour of such objects. The plant provides them with no reward and they leave quickly unless it has traps to slow them down. Such plants are far less common than myophilous ones Beetle pollination (cantharophily) • Beetle-pollinated flowers are usually large, greenish or offwhite in colour and heavily scented. Scents may be spicy, fruity, or similar to decaying organic material. Most beetlepollinated flowers are flattened or dish shaped, with pollen easily accessible, although they may include traps to keep the beetle longer. The plant's ovaries are usually well protected from the biting mouthparts of their pollinators. Beetles may be particularly important in some parts of the world such as semi-arid areas of southern Africa and southern California and the montane grasslands of Kwa-Zulu Natal in South Africa. Magnolia soulangeana Bird pollination (ornithophily) • Although hummingbirds are the most familiar nectar-feeding birds (as seen on TV), there are analogous species around the world: sunbirds, honeyeaters, flowerpeckers, honeycreepers, bananaquits, flowerpiercers, lories and lorikeets. Hummingbirds are the oldest group, with the greatest degree of specialization on nectar. Flowers attractive to hummingbirds that can hover in front of the flower tend to be large red or orange tubes with a lot of dilute nectar, secreted during the day. Since birds do not have a strong response to scent, they tend to be odourless. Perching birds need a substantial landing platform, so sunbirds, honeyeaters, and the like are less associated with tubular flowers. Rhododendron thomsonii Bat pollination (chiropterophily) • Bat-pollinated flowers tend to be large and showy, white or light coloured, open at night and have strong odours. They are often large and bell-shaped. Bats drink the nectar, and these plants typically offer nectar for extended periods of time. Sight, smell, and echo-location are used to initially find the flowers, and excellent spatial memory is used to visit them repeatedly. In fact, bats can identify nectar-producing flowers using echolocation. In the New World, bat pollinated flowers often have sulphur-scented compounds, but this does not carry to other parts of the world. Bat-pollinated plants have bigger pollen than their relatives. Cobaea scandens Ranunculaceae • • • • • • • • Includes: Ranunculus Trollius Anemone Hepatica Aconitum Delphinium Thalictrum Ranunculus repens Trollius europaeus Anemone blanda Hepatica triloba Aconitum vulparia Delphinium Thalictrum minus Primulaceae • • • • • • Includes: Primula Androsace Dionysia Cyclamen Dodecatheon Primula griffithii Androsace pyrenaica Dionysia aretioides Cyclamen creticum Dodecatheon alpinum