Largest trees up to 115 m short shoots needles in

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Unformatted text preview: ther spirally, in opposite pairs or in whorls of 3 or 4   On young plants, the leaves are needle-­‐ like, becoming small and scale-­‐like on mature plants of many genera   Female cones small, either woody or “berry-­‐like”   Includes: cypress, junipers, thuja, redwood (largest trees, up to 115 m)   “Short-­‐shoots”: needles in bundles   Needles retained for 2-­‐4 or more years   Pine needles adapted to dry condi�ons   Secondary growth begins early Epidermis (waxy cuticle) Resin duct sunken stomata Fig. 18-14 Cedrus atlantica Other conifers: Yew family (Taxaceae)   Many-­‐branched, small trees and shrubs   Leaves are spirally arranged, o�en twisted at the base to appear 2-­‐ ranked   Plants are dioecious   Ovuliferous scale develops into a fleshy aril partly enclosing the seed (not a fruit!)   Bird dispersed   Seeds and leaves toxic! Other conifers: Araucaria family (Araucariaceae)   Ancient family of conifers   Now only found in the Southern Hemisphere   Horizontal, spreading branches grow in whorls   Several species are popular ornamental trees (monkey-­‐ puzzle tree, Norfolk Island pine) 6 Male sporangia and gametophyte Conifer (pine): reproduc�on   Sporophylls are born on cones (strobili)   Male cones: simple with short unbranched axis that bears microsporophylls   Female cones: compound with short axis bearing cone bracts   Male and female cones on same tree (conifers) female male   Microsporophylls bear 2 microsporangia   Each microsporangium contains many sporocytes   Each microsporocyte produces 4 haploid microspores (meiosis)   Each microspore develop into a pollen grain (male gametophytes)   No antheridium! Pollen grain Fig. 18-22 Microsporangium with microspores Reduc�on in size of gametophytes prothallial cells generative cell Pinus pollen grain, 4-­‐celled, ca. 40 um No longer free living tube cell wings Fig. 18-18a Female sporangia and gametophyte (conifers)   Female (ovulate) cones larger and more complex than pollen-­‐bearing cones   Reduced branch systems (seed-­‐scale complexes)   Megasporophylls are fused into an ovuliferous scale that bears two ovules Horsetail gametophyte (bisexual), mul�cellular, ca. 3 mm Free living 7 Female sporangia and gametophyte (conifers)   Megasporocytes are cells contained within the ovule   Produce four megaspores by meiosis   Three of the megaspores die   The re...
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