Review of Algae, Bryophytes, Pteridophytes- Common Links Between Each Group of Plants

Algae

The algae can be described as non-vascular, non-embryophytic plants; meaning that they lack xylem, phloem and perhaps most importantly, an archegonium. All other plant groups (classified together as the Embryophytes) have a true archegonium. In lab and lecture we saw three main groups of algae, distinguished by the following characteristics:

Primary photosynthetic pigments, Storage product, cell wall composition, type and location of flagella. The embryophytes and one group of algae, the green algae (the chlorophyta) share the same characteristics: Chlorophyll a and b, carotenoids as photosynthetic pigments, starch as a storage product, cellulose cell walls, and whiplash flagella in pairs which are apical or sub-apical. Since one of our goals in the second half of the course is to link together the traits of the different groups of plants, this is significant.

Within the green algae, there is a class called the Charophyceae which is believed to be closely related to the embryophytes because they tend to be oogamous and have phragmoplastic cell division which are also traits found in the embryophytes. Two genera, Chara and Coleochaete are thought to be particularly close in relation to an embryophyte common ancestor, because they have other features one might find in a ancestor to the embryophytes: tissues which can be Parenchymatous, and a pseudo-archegonium; which functions similarly to a true archegonium, yet lacks features found in true archegonia. These two genera also have a haplobiontic, haploid life cycle, while all embryophytes have a diplobiontic (Alternation of Generations) life cycle

Summary: Chara and Coleochaete share features with The Embryophytes: The four criterea found in all green algae, oogamy, phragmoplastic cell division, some capacity to make parenchyma (in Coleochaete, at least). Yet they lack true archegonia, and a diplobiontic life cycle, which are features of all Embryophytes.

EMBRYOPHYTES

Bryophytes.

The Bryophytes are non-vascular embryophytes, meaning that they have true archegonia, alternation of Generations, and true parenchyma. They lack true xylem and phloem. The dominant generation in their life cycle is the gametophyte. The sporophyte is not a free living plant, and in most cases it's growth is determinate. All other embryophytes are vascular plants. In all vascular plants, the sporophye is the dominant generation in the life cycle. A feature of a common ancestor of bryophytes and vascular plants would be a sporophyte with indeterminate growth, and the development of true vascular tissue.

There are three groups of Bryophytes: Mosses, Liverworts, and Hornworts. Unlike the algae, we cannot point to a particular class of bryophyte and say that that group is closely related to a common ancestor. We find both ancient and derived features in each group.

Mosses:

Ancient- early gametophyte growth is filamentous (protonema) similar to filamentous algae.

Derived- Hydroids and Leptoids, which are vascular tissues analogous to true xylem and phloem.

Liverworts: liverworts really have no features which are decidedly ancient or derived.

Hornworts:

Ancient- Cells contain one chloroplast, and also a pyrenoid. These are features found in the green algae.

Derived- The sporophyte has an intercalary meristem, and therefore the cpacity for indeterminate growth.

Summary: Bryophytes have Archegonia, Alternation of Generations life cycle, plus other Embryophyte features found in Carophycean Algae (listed above). They lack true Vascular Tissue and a free living sporophyte with indeterminate growth.

Pteridophytes

Pteridophytes are a diverse group of plants. They are the free sporing vascular plants. They have true Vascular tissue, the Sporophyte dominates the life cycle, yet lack seeds.

Because they are so diverse, one cannot point to a common ancestor to the Pteridophytes. However, There is a feature found in all seed plants which is not found in all Pteridophytes. That is Heterospory and and endosporic gametophyte development. We did see this trait in Selaginella, a lycopod. Lycopods, however are not directly related to seed plants. Some ferns also are heterosporous.

Seed Plants

True seed plants have ovules- integumented megasporangia. They do not shed megaspores. Instead they are retained within the megasporangium (the nucellus) where fertilization and embryo development takes place.

Gymnosperms are the naked seed plants. Their ovules are exposed, unlike Flowering plants, whose ovules are protected within a carpel(ovary) which will ultimately develop into a fruit. Gymnosperms do not make fruits. Flowering Plants also perform double fertilization- they make nedosperm. Gymnosperms do not do this; instead the parent megagametophyte provides nutrients to the developing embryo.