Taxonomy and Plant Diversity: Algae, Fungi, Bryophytes, Pteridophytes and Gymnosperms
This domain is examined mainly through identification: you are given a set of characters and must place the plant in the correct group and justify the placement. The characters that decide the answer are pigments and storage products in algae, mycelium and spore type in fungi, and gametophyte–sporophyte dominance in the embryophytes.
Core rules
- Algae - Chlorophyceae (chlorophyll a and b, starch, cellulose wall; Spirogyra, Chara), Phaeophyceae (chlorophyll a and c, fucoxanthin, laminarin and mannitol, cellulose with algin; Sargassum), Rhodophyceae (chlorophyll a and d, phycoerythrin, floridean starch; Gelidium, Polysiphonia).
- Fungi - Phycomycetes (coenocytic hyphae, zoospores; Rhizopus), Ascomycetes (ascospores in an ascus; Aspergillus, Penicillium), Basidiomycetes (basidiospores; Agaricus, Puccinia), Deuteromycetes (no sexual stage; Alternaria).
- Bryophytes - gametophyte dominant, sporophyte dependent on it; Marchantia is thalloid with upright gametophores, Funaria is leafy.
- Pteridophytes - sporophyte dominant with the first true vascular tissue; Selaginella is heterosporous and ligulate; Salvinia is an aquatic fern.
- Gymnosperms - ovules naked, no ovary and therefore no fruit; Cycas has coralloid roots and circinate vernation, Pinus and Gnetum are the other standard examples.
Worked example
A specimen is thalloid and dorsiventral, bears rhizoids, and carries a stalked umbrella-shaped structure with finger-like hanging lobes. Reasoning: no vascular tissue, so it is a bryophyte; thalloid with rhizoids, so Marchantia; the umbrella is the archegoniophore because the lobes hang downward and bear archegonia. The antheridiophore is a flat-topped disc instead.
Traps that cost marks
Writing laminarin for red algae and floridean starch for brown; calling Selaginella homosporous; stating that gymnosperms bear fruit; labelling Salvinia a bryophyte because it floats.