Gymnosperms: Conifers I & II

Conifers I: Gymnosperms

  • Vascular plants—plants with xylem and phloem and vascular bundles

    • ferns

    • gymnosperms—1000 species

    • angiosperms—233,000 species

  • Gymnosperms: seed plants bearing “naked seeds,” which are ovules exposed at pollination

  • Gymnosperms originated about 250 MYA as the first seed plants, and reached their peak of diversity during the Mesozoic Era, 250-100 MYA

  • Gymnosperms—12 plant families, 88 genera, 1000+ species

    • Conifers (‘cone-bearing’)—600+ spp.

      • Pinus—about 100 spp., n. hemisphere

    • Ginkgo—1 species

    • Cycads (palms)—(tropical)—300+ spp.

      • Zamia

    • Gnetum (genus) (also tropical) (100 spp.)

Literary quote of the week, from The Overstory, by Richard Powers (have you read it? Put it on your Winter Break reading list!):

"It's the long species of the only genus in the sole family in the single order of the solitary class remaining in a now-abandoned division that once covered the earth--a living fossil three hundred million years old that disappeared from the continent back in the Neogene and has returned to scratch out a living in the shadow, salt, and fumes of Lower Manhattan. A tree older than conifers, with swimming sperm and cones that can put out a trillion and more grains of pollen a year. In ancient island temples on the other side of Earth, thousand-year-olds, molten and blasted, close to enlightenment, swell to incredible girth, their elbows growing back down from giant branches to re-root into new trunks of their own. A tree like this grew on the street just outside the house of the man who ordered the bombing of Hiroshima, and a small few of them survived that blast. The fruit flesh has a smell that curdles thought; the pulp kills even drug-resistant bacteria. The fan-shaped leaves with their radiating veins are said to cure the sickness of forgetting...He remembers. He remembers. Ginkgo. The maidenhair tree....
There, as he watches, the whole tree bares. It falls from one moment to the next, the most synchronized drop of leaves that nature ever engineered. A gust of air, some last fluttered objection, and all the veined fans let go at once, releasing a flock of golden telegrams down West Fourth Street."

Conifers (and ginkgo) in FOR 401

  • Pinaceae

  • Cupressaceae

  • Ginkgo (not technically a conifer)

Conifer foliage

  • Pinus (pine)

    • Leaves (needles are acicular, or needlelike

    • Needles are borne in bundles called fascicles

    • The buds are inside the fascicle and usually aborted

    • The number of needles per fascicle is diagnostic

      • Pinus taeda, Pinus echinata, Pinus strobus?

  • Tsuga (hemlock)

    • Short, single, flat needles

    • Needles attached to branches with a short peg, or petiole

    • Rows of white stomata on the undersides of the leaves

  • Picea (spruce)

    • Needles are borne singly on small bumps, called sterigmata (plural singular is a sterigma)

    • Spruce is sharp

    • In NC we have red spruce, Picea rubens. We also learn Norway spruce.

  • Abies (fir)

    • Blunt-tipped, flat needles

    • ‘Fir is flat’ or ‘fir is friendly’

    • Also has rows of white stomata on undersides of needles

  • Larix (larch)

    • Deciduous

    • Needles borne in clusters on short spur shoots

  • Cupressaceae

    • Bark on mature trees in fibrous and shreddy

    • Many species have flat and scale-like leaves. Others have small branchlets and needles

    • Cones have branchlets and needles

    • Cones have peltate scales (more later)

    • Metasequoia and Taxodium are deciduous

Conifers II

  • Two types of cones

    • Species in Pinaceae have flat-scaled cones

    • Species in Cupressaceae have peltate-scaled cones

Conifer reproduction

  • Considers don’t flower!

  • Male and female cones are separate structures

    • Microsporangiate strobilus—male cone

      • =micro/small + spot/spore + angiate/vessel, strobilus/cone

    • Megasporangiate (or macrosporangiate) strobilus—female cone

      • mega/large + spor/spore + angiate/vessel, strobilus/cone

  • Strobilus=cone

    • Plural of strobilus=strobili

  • Male cones

    • Central axis of strobilus in stem tissue

    • Scales are leaf tissue

  • Female cones: all stems tissue; the female cones are short shoots

  • 2 seeds per cone

  • Microsporgania

    • Male cone is much smaller than female cone

    • Microsporangia are borne in pairs at the base of papery scales

    • Contain many diploid microsporocytes (=microspore mother cells) that form the pollen

  • Pollen from pines are too big to be allergens

Pollination and fertilization

  • Pollination in conifers takes place with wind, in the spring

  • Once pollen reaches female cones:

    • Pollen can slide down bract

    • Pollination droplet in ovule may pull or float pollen in

    • Pollen may germinate and grow to ovule

  • Bracts help transfer pollen to the scales

Megasporangia

  • apophysis: end of cone scales; lighter in color and exposed when cone is closed

  • umbo: a protuberance at the center of the apophysis

  • prickle: an umbo shaped like a point

    • cones that have prickles are said to be “armed”

    • the winged seeds sit on top of the scale

  • Peltate scales have 2-9 seeds per scale

  • Bract is fused to the cone scale

  • Scales are fused to a central point or axis

Conifer reproduction cont.

  • “Fleshy” cones

  • Juniperus: dioecious

  • Abies (firs), Taxodium (cypress), and Cedrus (cedar) have deciduous cones

  • Other species have intact cones that open on the tree or drop to the ground

Seed dispersal

  • Cones open and close in response to relative humidity

  • Most scales are two layers, top and bottom

  • The top layer shrinks only 1% in lower humidity

  • The bottom layer shrinks 20%, pulling the cone scale down and open

  • Most conifers are wind-dispersed, cones open in dry weather and seeds are released

  • Taxodium seeds float on water

  • Juniperus seeds are animal dispersed

  • Pinus edulis, which grows throughout much of the West, has extremely nutritious and tasty pine seeds, which have been harvested by many Indigenous tribes (through modern times) as an important food source. They are called pignolia nuts in Italy and are an important ingredient in pesto.

Serotinous cones

  • Serotinous cones open late

  • Usually found in species that regenerate after a catastrophic fire

  • Cones are sealed shut with resin that requires fire to melt