Conifers & Gnetophyta

• Coniferophyta: include tallest and oldest living vascular plants, 2 extinct orders (cordaitales & voltziales), 1 living order (coniferales)
• Cordaitales: easiest conifers 300-260 MY BP, widespread, monopodial, eustele (large pith, dense wood), secondary growth, leaves wide, monoecious, both male and female strobili compound cones
• voltziales: 285 - 180MY BP, monopodial, whorled branches, needle leaves, male strobili simple, female strobili compound
• coniferales: extant order of conifers, 225 MY BP- present, 7 families, 70 genera, 630 species, mainly temperate to boreal
• coniferales shoots: monopodial, eustele, lots of secondary xylem (tracheas with ray parenchyma), long shoots, shoots may extend from buds formed the previous growing season (determinate growth) OR primordia formed completely in the current growing season (indeterminate growth)
• coniferales buds: simple (only leaf or cone primordia enclosed by bud scales) or compound (main bud contains short shoots, branch and/or cone primordia and scales)
• coniferales leaves: simple often needle like or linear or scale like or broad, phyllotaxy - often spiral or opposite or whorled, venation - usually parallel or mid vein or dichotomous, most are perennial
• coniferales leaves: some have heteroplastic development (different juvenile and adult leaves), a few have cladophyll, xerophytic
• coniferales roots: mycorrhizal associations are important to get nutrients out of soil, a few species have pneumatophores (structures that grow upwards from roots - provide oxygen to bottom)
• coniferales reproduction: most monoecious, most form unisexual strobili (pollen cones - simple, seed cones - compound), naked seed
• Pinaceae pollen development: microsporangiate strobili (pollen cone) is a simple strobili, initiated on branches, microsporangia on lower side of microsporophyll
• Pinaceae pollen development: sporogenous cells (2n) undergo mitosis to form microspore mother cells (2n) which undergo meiosis to form 4 microspores (1n) per microspore mother cell, each microspore divides to form pollen grain (microgametophyte)
• coniferales pollen grains are small but numerous
• coniferales pollination: female receptive period (before meiosis in seed cone), pollen sacs rupture and release pollen which is transferred by wind to cone, cone scales close
• pollination mechanisms in coniferales: pollination drop, pollen captured by integument , pollen captured outside ovule (pollen germinates outside micropyle)
• Pinaceae ovule development: megaspore mother cell (2n) undergoes meiosis to form 4 megaspores (1n), where 3 degenerate and 1 functional megaspore undergoes free nuclear division, then cell walls form and a megagametophyte (1n) forms with archegonia (egg)
• pinaceae fertilization: pollen germinates in micropyle, pollen tube grows between neck cells, discharges contents into archegonium, large male gamete fuses with egg nucleus, second male gamete and other nuclei degenerate
• pinaeceae embryogeny: zygote undergoes 2 free nuclear divisions (4 free nuclei), nuclei migrate to base of archegonium, cell walls form, apical cells form pro embryo, suspensor cells elongate and push pro embryo through archengonial jacket into corrosion cavity in megagametophyte (early embryo)
• Simple polyembryony: one embryo from each of several archegonia (embryos genetically different)
• cleavage polyembryony in pines: columns of cells in proembryo split (4 embryos per archegonium - all genetically identical) , post zygotic selection , 1 dominant embryo
• Pinacea embryo development: embryo and cone mature, hard seed coat develops, cone and seed desiccate, and seed shed
• Conifers have 7 families: Pinaceae, Araucariaceae, Podocarpaceae, Sciadopityaceae, Cupressaceae, Taxaceae, and Cephalotaxaceae
• Pinaceae: 11 genera, 232 species (pines, spruce, Douglas fir, hemlock, true firs), woody cones with separate bracts and scales, two inverted ovules per scale
• Pinus (pine): leaves borne in fascicles (bundles), buds compound, winged pollen grains and seeds, soft pines (5 leaves) and hard pines (3 leaves)
• Picea (spruces): short needles on woody bases, woody cones
• Abies (true firs): upright mature woody cones with deciduous scales, flattened needles, rounded buds
• Pseudotsuga (Douglas fir): pointed buds, needles surround branch, thick fire resistant bark, prominent 3 pronged bract (look like mouse)
• Tsuga (hemlock) : needles uneven lengths, tiny cones
• Larix (Larches): deciduous needles on short shoots (clusters of 10), woody cones (elongated bracts)
• Cedrus (true cedars): needles in clusters on short shoots, mature upright woody cones with deciduous scales
• Cupressaceae: 30 genera, 142 species, often scale like leaves, western red cedar, junipers, yellow cedar
• Juniperus (junipers): dioecious plant, shrubby, usually scale leaved, fleshy strobili, smells like gin
• Thuja plicata(Western Red Cedar): woody cones, needles scale like, fibrous bark
• Callitropsis nootkatensis (yellow cedar): fleshy round cones, prickly branches, yellow pollen cones, flexible fibrous bark
• Podocarpaceae: 18 genera, 173 species, dioecious, naked seed on fleshy receptacle, winged pollen, spiral leaves
• Araucariaceae: 3 genera, 40 species, broad leaves, monoecious and dioecious species, 5-20 microsporangia per microsporophyll,
• Taxaceae: 4 genera, 17 species, dioecious, seed in arils (red fleshy structure), linear leaves
• Cephalotaxaceae: 2 genera, 10 species, dioecious, opposite branching, fleshy outer layer of seed coat
• Sciadopityaceae : umbrella pine, 1 genus, 1 species, two fused leaves on short shoot, cones with fan shaped scales
• Gnetophyta are gymnosperms with features of both conifers and angiosperms