Angiosperms Summary

Angiosperms

  • Only one division: Angiospermae
  • Flowering plants with seeds enclosed in a structure.
  • Angio = enclose, Sperma = seed
  • Divided into two classes: Dicotyledons and Monocotyledons

Characteristics of Angiosperms

  • Trees, shrubs, or herbaceous plants.
  • Vessels and tracheids in wood; hardwood in trees.
  • Micro- and megasporophylls arranged in flowers.
  • Seeds enclosed inside a fruit (ovary).
  • Fruit made of united megasporophylls (carpels).
  • Microsporophylls modified to form stamens.
  • Sterile sporophylls (perianth) often present to attract insects for pollination.

Angiosperm Reproduction

  • Female gametophytes are very reduced (8-500 cells).
  • No archegonia or antheridia.
  • Double fertilization occurs:
    • One male nucleus fuses with a haploid egg to form a zygote.
    • The second male nucleus fuses with 2 polar nuclei to form a triploid (3n) endosperm.

Class: Dicotyledons

  • Two cotyledons in the seed.
  • Flower parts in fours (tetramerous) or fives (pentamerous) or multiples.
  • Perianth usually divided into petals and sepals.
  • Leaves simple or compound with reticulate veins and a central midrib.
  • Vascular tissue in the stem arranged in a ring.
  • Have vascular cambium and most form hard woods.

Class: Monocotyledons

  • One cotyledon in the seed.
  • Flower parts in threes (trimerous) or multiples of three.
  • Perianth usually not divided into petals and sepals.
  • Leaves with parallel veins; no central midrib.
  • Vascular tissue scattered in stems.
  • No cambium, no hard wood; mostly herbaceous.

Vegetative Morphology: Leaves

  • Leaves are the main photosynthetic organs.
  • Leaf types:
    • Simple: a leaf with a single blade.
    • Compound: more than one blade, small blades called leaflets.
  • Arrangement on a stem:
    • Alternate: single leaf on a node.
    • Opposite: paired leaves on a node.
    • Whorled: three or more leaves on a node.

Leaf Modifications

  • Scales: small/thin, papery structures.
  • Tendrils: thread-like for attachment.
  • Spines: sharp/pointed.
  • Succulent: thick and water-storing.

Stem Modifications

  • Rhizome: underground creeping, horizontal stems.
  • Tubers: thick, fleshy underground stems for food storage and reproduction.
  • Bulbs: upright, underground stems, surrounded by thick, fleshy scale leaves.
  • Stolon: creeping stem, above ground, producing roots at nodes.
  • Tendrils
  • Spines
  • Cladophylls: flattened, photosynthetic stems.

Roots

  • Tap root system: dicots.
  • Fibrous root system: monocots.
  • Root modification: storage roots.