BOTANY VOLUME 3 - EVOLUTION AND SYSTEMATICS - 2007

11. SYSTEMATICS AND PHYLOGENY

11.2. Bacteria, Fungi, Plants

Seventh subkingdom: chlorobionts (Chlorobionta, "Viridiplantae")

Chlorobionta contain chlorophylls a and b in their pure green Plastids. This combination of assimilatory pigments is found in prochlorobacteria (see kingdom Bacteria), and According to the latest data, also in cyanobacteria (see kingdom Bacteria) and, among Algae, in chlorarachniophytes (see Appendix 1 to Chlorophyta) and euglenophytes (see APPENDIX 2 to Chlorophyta), which, however, differ in other characteristics, in particular, the absence of starch as a storage substance. Carotenes and xanthophylls (see Table 11.2) do not mask the green color of the assimilatory pigments. METABOLISM/14.html">Chloroplasts are bounded only by a double membrane, without an Endoplasmic reticulum or a girdle lamella (see Fig. 11.72, G). Thylakoids are grouped into stacks—grana. Pyrenoids, if present, are located inside the chloroplast.

The most important storage polysaccharide is starch, which is deposited as free-lying grains near the pyrenoid inside the chloroplast. Sometimes, a significant amount of fat is also deposited in the Cells. The Cell wall consists of polysaccharide fibrils (mainly Cellulose and partly mannan and glucan) embedded in an amorphous, often mucilaginous fraction. The wall is most often formed directly on top of the Plasmalemma (unlike in dinophytes and diatoms). The amorphous fraction usually consists of various Polysaccharides—Pectins¹.

¹ Some members of the subkingdom have a different composition, for example, peptidoglycan (as in green algae of the genus Chlamydomonas). — Translator's Note.

In some terrestrial algae among the Chlorobionta, a resistant substance, sporopollenin (see 2.2 7.6), has been found; it also occurs in higher plants belonging to the same subkingdom, making their spores and pollen resistant to desiccation².

² Sporopollenin is also present in green algae living in Water (for example, in Chlorella species). — Translator's note.

In chlorobionts, in contrast to most of the previously discussed groups of algae, forms with a highly differentiated Structure are also frequently found in brackish and fresh waters. In this subkingdom, the transition to higher land plants occurred.