B140: Seed Plants (2024)

Vascular plants with naked seeds ("gymnosperms") are placed in five or more phyla(divisions): seed ferns (Pteridospermophyta), cycads (Cycadophyta),ginkgos (Ginkgophyta), conifers (Coniferophyta), and Gnetophyta.
Angiosperms (flowering plants) have seeds enclosed in an ovary.
Flowers include ovaries and surrounding structures.
Ripened ovaries make up a fruit.
Roots, stems, and leaves reach maximum complexity and diversity within the angiosperms.
Angiosperms are divided into"dicots" (Dicotyledonae) and "monocots" (Monocotyledonae).Review: Vascular plant parts

Seeds are easily dispersed structures developed from a zygote andenclosing an embryonic sporophyte.
All plants with seeds also possess megaphylls,leaves with branched veins whose bases interrupt the vascularbundle to form a leaf gap.

Gymnosperms: Vascular plants with naked seeds, borne naked on the surface of reduced, scale-like leaves and not enclosed within ovules(as in angiosperms).

Seed ferns (Pteridospermophyta): Extinct plants with large,fern-like leaves, but reproducing by seeds; occasionally growing tothe height of small trees. Devonian to Jurassic in age, dominantduring the Carboniferous (when they formed great coal swamps). Believedclose to the ancestry of other seed plants.

Cycads (Cycadophyta): Short, thick-stemmed plants with a crownof large fern-like or palm-like leaves. Seeds borne together in a structureresembling a large pine cone. Flourished during the Mesozoic era; onlya few tropical and subtropical genera persist today.

Ginkgos (Ginkgophyta): A mostly Mesozoic group with one livingspecies (Ginkgo biloba, an ornamental tree with fan-shaped leaves).

Conifers (Coniferophyta): The most familiar and economically importantgymnosperms, including pines, spruces, firs, etc. Leaves are typically scale-like or needle-like, with reduced surface area. Seeds are borne incone-like aggregates.

Gnetophyta: This group includes only three living genera (Gnetum,Ephedra, Welwitschia), which differ greatly. All share a partiallyenclosed type of seed that approaches the angiosperm condition but wasprobably derived independently.

Plants C
Angiosperms: Flowering plants, with seeds enclosed in a protectiveovary.
Many flowers are fertilized by insects.
Angiosperms probablyevolved in response to selection by insects.

Flower: An ovary, together with surrounding reproductive structures:

• Petals and sepals surround and protect the other flower parts, especially in undeveloped flowers. In many species, these parts may have colors or odors that attract insects or other species that pollinate the plant or disperse its seeds.
• Male flower parts include stamens, each made of a filament and a
  pollen-producing anther. Pollen grains contain male gametophytes.
• Female flower parts include stigma (whose sticky surface catches pollen), style (a stalk-like part supporting the stigma), and ovary, enclosing one or more ovules within modified leaves called carpels. Each ovule develops into an 8-celled gametophyte containing 1 egg, 2 polar nuclei, and 5 other cells.
• "Complete" flowers have all the parts listed above, but many species have separate male flowers and female flowers.

Fertilization: First, a thin, long pollen tube grows from thepollen grain down the style. Two nuclei (tube nucleus and generativenucleus migrate down the pollen tube as it grows. The generative nucleusthen divides into two sperm cells: one fertilizes the egg (syngamyor true fertilization; the other fuses with the 2 polar nuclei to forma triploid (3N) endosperm, containing stored food that supports theembryo later. This so-called double fertilization is characteristicof all angiosperms. After fertilization, the new embryo and its endospermand protective coverings make up a seed.

Fruits: One or more ripened ovaries together constitute a fruit,enclosing one to many seeds. Many fruits are eaten (and their seeds dispersed)by animals; other seeds are dispersed by wind, etc.

Types of fruits
Flowers that mimic bees

Roots: Absorptive parts, usually underground. They contain, from theoutside inward:

• Epidermis, from which absorptive root hairs develop.
• Cortex, often a thick layer.
• Endodermis, containing a waterproof Casparian strip.
• Vascular bundles, with xylem, phloem, and cambium surrounded by a pericycle.

Stems: Supportive structures which contain, from the ouside inwatrd:

• Epidermis
• Cortex (bark)
• Vascular bundles, each containing phloem and xylem, along with some persistently embryonic tissue called cambium.
• Pith (not always present) in the innermost parts of the stem.

Leaves: The major photosynthetic organs, are described here.Specialized leaves: Mimosa sensitive plant

Class Dicotyledonae ("dicots", Magnoliophyta): Angiosperms with aseed containing two "seed leaves" (cotyledons) in which food isstored. (The two halves of a dried peanut are a familiar example.)

• Flower parts are usually in multiples of 4 or 5.
• Veins in leaves and petals branch to form net-like patterns.
• Vascular bundles usually arranged in a circular ring.
• Includes the majority of angiosperms: buttercups (considered primitive), roses, beans (and other legumes), daisies, oaks, maples, apples, oranges, peaches, melons, and many others.

Class Monocotyledonae ("monocots," Liliophyta): Angiosperms with aseed containing only one "seed leaf" (cotyledon) in which food is stored(such as a kernel of corn, which cannot be divided into halves).

• Flower parts are usually in multiples of 3 or 6.
• Leaves and petals have parallel veins that branch only occasionally.
• Vascular bundles usually scattered throughout cross-section of stem.
• Includes the more advanced angiosperms: orchids, lilies, palms, and grasses (including wheat, corn, rice, and other cereal grains).

REVIEW: Study guide and vocabulary