Introduction to Plant Classification:
- Plant classification has evolved from using external features to considering internal structures, chemistry, and evolutionary relationships.
- Early systems were "artificial," later systems were "natural," and modern systems are "phylogenetic."
- Modern taxonomy uses computers, cytology, and chemistry for more accurate classifications.
Algae:
- Algae are simple, chlorophyll-containing organisms that live mostly in water.
- They have a simple body structure called a thallus and are autotrophic.
- They reproduce vegetatively, asexually (by spores), and sexually (isogamous, anisogamous, or oogamous).
- They are important for carbon fixation, oxygen production, and as a food source in aquatic ecosystems.
- They are classified into three main groups: green (Chlorophyceae), brown (Phaeophyceae), and red (Rhodophyceae).
Chlorophyceae (Green Algae):
- Grass green due to chlorophyll a and b.
- Can be unicellular, colonial, or filamentous.
- Store food as starch in pyrenoids.
- Reproduce vegetatively (fragmentation), asexually (zoospores), and sexually (isogamous, anisogamous, or oogamous).
Phaeophyceae (Brown Algae):
- Primarily marine, olive green to brown due to fucoxanthin.
- Store food as laminarin or mannitol.
- Have a cellulosic wall with algin.
- Often have a holdfast, stipe, and frond.
- Reproduce vegetatively (fragmentation), asexually (biflagellate zoospores), and sexually (isogamous, anisogamous, or oogamous).
Rhodophyceae (Red Algae):
- Mostly marine, red due to r-phycoerythrin.
- Mostly multicellular with complex body organization.
- Store food as floridean starch.
- Reproduce vegetatively (fragmentation), asexually (non-motile spores), and sexually (oogamous).
Bryophytes:
- Small plants found in moist environments; called "amphibians of the plant kingdom."
- Plant body is a thallus; attach to the ground with rhizoids.
- Dominant gametophyte stage produces sex cells.
- Sporophyte depends on the gametophyte for nutrition and produces spores.
- Important ecologically for creating soil and preventing erosion.
Liverworts and Mosses:
- Liverworts have a flat, thalloid body and reproduce asexually using gemmae.
- Mosses have a two-stage gametophyte (protonema and leafy stage) and a more complex sporophyte.
- Both groups need water for sexual reproduction and produce spores.
Pteridophytes:
- First land plants with vascular tissue (xylem and phloem).
- Main plant body is the sporophyte with true roots, stems, and leaves.
- Reproduce by spores; some are heterosporous.
- Require water for fertilization and live in moist environments.
- Classified into four classes: Psilopsida, Lycopsida, Sphenopsida, and Pteropsida.
Gymnosperms:
- Seed plants with "naked" seeds (not enclosed in a fruit).
- Adapted to various environments, often with specialized leaves to reduce water loss.
- Heterosporous; gametophytes develop within the sporophyte.
- Pollination is by wind; fertilized ovule develops into a naked seed.
Angiosperms:
- Flowering plants with seeds enclosed in fruits.
- Most diverse group of plants; vital for human life.
- Classified into two major groups: dicotyledons and monocotyledons.