MEDICAL BOTANY - A.G. Serbin - 2003

SECTION 3. SYSTEMATICS

SUPERKINGDOM EUKARYOTES (NUCLEATED) — EUCARYOTA. KINGDOM PLANTS — PLANTAE

EMBRYOPHYTES (Embryophyta), or CORMOPHYTES (Cormophyta)

Higher plants comprise about 300,000 species. They are highly organized terrestrial organisms adapted to aerial habitats. Higher plants possess specialized systems of true vascular and mechanical Tissues, as well as a complex epidermal tissue system. Their vegetative body is differentiated into a SHOOT system (consisting of stem and leaves) that performs an assimilatory function, and underground Organs for mineral Nutrition — rhizoids or roots. Cell Plastids are characterized by the absence of additional specific pigments found in Algae. Sex organs (gametangia) and spore-bearing structures (sporangia) are multicellular formations. Their life cycle features a rhythmic Morphology/12.html">ALTERNATION OF GENERATIONS. A multicellular zygote develops into an embryo while still on the parent Organism.

Higher plants include spore plants (bryophytes, psilophytes, lycophytes, horsetails, ferns) and seed plants (gymnosperms, angiosperms). Evolutionary relationships among these plant groups are shown in Figure 3.3.

SEED PLANTS

It is widely accepted that seed plants evolved from heterosporous ferns as an ADAPTATION TO A terrestrial lifestyle. The evolutionary advantages of seed plants are as follows:

✵ microspores and megaspores give rise to male and female gametophytes, respectively, which develop on the sporophyte without leaving the spores and completely lose their independence;

✵ the Fertilization process takes place inside the female gametophyte and is therefore independent of liquid Water;

✵ As a result of fertilization, the ovule — a modified megasporangium — develops into a seed, which is a more efficient unit of species dispersal than a spore, protected by a seed coat and consisting of a new sporophyte embryo and nutritive tissue;

✵ the seed grows into a sporophyte — a heterosporous plant with a complex organ Structure.