TS Sexual/Asexual Reproduction

Sexual reproduction requires…

Fertilizations of pistils or female flowers by pollen from stamens or staminate flowers

Cross pollination characteristics

Need lots of pollen, better genetic diversity, risk if pollinators don’t find it, need to have lots of seeds (more energy)

Self pollination characteristics

Don’t need pollinators as much but no genetic flow (clones)

Phenotypic plasticity

Degree that a tree shows variable growth characteristics (determined by its environment)

4 reproductive structures of angiosperms

Petals, sepals, pistils, stamen

Petals

Bright coloured + sweet smelling to facilitate cross pollination

Sepals

Similar to bud scales, outermost layer, protect petals/reproductive organs

Pistil

Female reproductive part, consists of stigma/style/ovary

Stigma

Collects pollen, sticky landing pad

Style

Facilitates movement of pollen tube to ovary (fertilization)

Ovary

Produce ovules (seeds), matures into fruit

Stamen

Male reproductive part, consist of filamen + anther

Filamen

Elevates the anther, facilitates pollen transfer

Anther

Produces pollen grains

Complete flowers

Flowers that have all 4 parts (sepals/petals/pistil/stamen)

Incomplete flowers

Flowers that lack a part, usually sepals or petals

Perfect flowers

Both stamen (male) and pistil (female) parts on one flower but can lack sepals/petals (cherries)

Imperfect flowers

Lack either stamen or pistil parts, unisexual (oaks)

Monoecious arrangement

Imperfect male and female flowers together one on tree (pines)

Dioecious

Imperfect male and female flowers on separate trees (white ash)

Trimonoecious (polygamous) arrangement

Perfect flowers AND male or female imperfect flowers on the same tree (sugar maple)

Polygamo-dioecious

Primarily dioecious but may be individuals that are polygamous (red maple)

What do male cones do

Produce pollen that fertilizes female (woody) cones

Cones

Characteristic of pines/larches/spruces

Aril

Seed cone scale that’s modified to surround the seed in a fleshy cup (yews)

Juniper berries

Female seed cones with modified fleshy scales that are fused to look like a berry

Indehiscent fruits (dry)

Don’t split open when mature, fall from tree as is (nuts - oaks/hazelnuts)

Dehiscent fruits (dry)

Split open when mature, legumes (honey locust) (conifer cones)

Drupe (stone fruits) (fleshy)

Single stoney seed encased in flesh (cherry)

Pome (fleshy)

Fleshy fruits with fibrous cores and multiple seeds (apples)

Drupaceous nuts (fleshy)

Seeds that share characteristics of nuts and drupes, seed encased in fibrous outer shell (rather than hard) (walnuts)

Seed masting

When a species produces seed one year but then go multiple years before again

Reasons for seed masting

Biological expense of seed production, predator satiation hypothesis, pollinator efficiency hypothesis, pathogen escape hypothesis

Predator satiation hypothesis

Overwhelm the system so predators can’t eat them all (oaks)

Pollinator efficiency hypothesis

Trees set all flowers at same time so more flowers so more cross pollination

Pathogen escape hypothesis

Like crop rotations, if a host plant is gone for a pathogen that transfers through seeds, it will die out

Periodicity

Interval between good crop years, differs by species

What is needed to have a good seed crop

Lots of flowers and pollen, multiple mature trees to contribute to gene pool

Main adaptations to avoid self pollination

Flower arrangements (imperfect), location of male and female cones

Secondary adaptations to avoid self pollination

Dichogamy, herkogamy, self-incompatibility, reduction in nectar production

Dichogamy

Make the anther and stigma mature at different times

Herkogamy

Stigma location is elevated above anthers

Self incompatibility

Genes in stigma can reject pollen / not allow pollen tube to form

Ortet

Originally sexually reproduced plant

Ramet

Offspring produced asexually/vegetatively

Adventitious buds

Found below the bark on stem/branches and roots/root collar

What makes adventitious buds active

Wound/stress, increased sunlight, growth regulators (auxin:cytokinin ratio)

Coppicing

Cutting the tree close to the base in winter so shoots grow rapidly from bottom

Pollarding

Cutting off all the branches so shoots make crown look funny shape

Root collar sprouts

Buds form on root collar at base of tree

Root sprouting

Buds form on roots and create new trees

Fragmentation

Take part of a tree and it will root to create a new tree

Stolons and runners

Producing a runner (looks like a root but above ground), where it meets the ground again it roots and creates a node and forms a new plant, over time the runner dies and the plants separate

Layering

Low branch is trapped on the ground, branch produces adventitious buds, buds root, branch is phototropic and grows, branch doesn’t die, stays connected to larger tree (conifers)

Tipping

When a large tree falls on a young one and the apical stem cells make adventitious buds which make roots

Plus trees

Superior phenotype, assumed superior genotype, specifically selected for growing stock

Human use for vegetative reproduction

Scions (cuttings) from trees to preserve or make cultivars, grafts