Botany and Plant Science

Both Riccia and Marchantia (liverworts) have unicellular, unbranched rhizoids. These can be either smooth-walled or tuberculate, but they are always single-celled and do not branch.

When a moss spore germinates, it first produces a filamentous, branched, green, and algal-like juvenile stage called the protonema, from which the leafy gametophores later develop.

The sporophyte of Anthoceros is unique because it possesses a basal intercalary meristematic zone situated between the foot and the capsule, which allows for continuous, indeterminate growth of the sporophyte.

In Anthoceros, the ventral surface of the thallus contains slime pores (mucilage clefts) through which mucilage is secreted, and these pores also serve as entry points for symbiotic Nostoc colonies.

The stem (axis) of the Funaria gametophyte is covered by a single-layered epidermis. This epidermis lacks both a protective cuticle and stomata, which allows for direct absorption of water and gases. Stomata in Funaria are only found on the apophysis of the sporophytic capsule.

Paraphyses are sterile, multicellular, uniseriate hair-like structures found interspersed among the sex organs in the receptacles of mosses. They help in retaining water through capillary action and protect the developing sex organs from drying out. Apophysis and hypophysis, on the other hand, refer to parts of the sporophyte capsule.

Peristome teeth are specialized structures found at the mouth of the moss capsule. They are hygroscopic, meaning they bend outwards or inwards in response to changes in humidity, which actively aids in the gradual dispersal of spores. Other parts like the columella provide support, while the operculum acts as a lid.

The columella is a central, sterile column of parenchymatous tissue found in the capsule of mosses. It provides structural support to the surrounding spore sac and helps in the conduction of water and nutrients to the developing spores.

In the fern Dryopteris, the sporangium wall has a specialized ring of cells with differentially thickened walls called the annulus. As the sporangium dries, the tension in the water inside the annulus cells causes them to contract, eventually tearing open the sporangium at the stomium to release the spores.

The gametophytic phase of Riccia begins with the haploid spore, which germinates to form the vegetative thallus. This thallus produces male and female gametes in the antheridia and archegonia, and their fusion (fertilization) results in the formation of a diploid zygote, which marks the end of the gametophytic phase.

Polytrichum is a genus of mosses, and its sporogonium (sporophyte) is differentiated into three distinct regions: the foot (which anchors it to the gametophyte and absorbs nutrients), the seta (a long stalk), and the capsule (where spores are produced). This tripartite division is characteristic of advanced bryophyte sporophytes.

In Riccia, the sporophyte is extremely simple, consisting only of a capsule that remains permanently embedded within the tissue of the gametophytic thallus. Because it lacks any specialized dehiscence mechanism like elaters or peristome teeth, the spores are only released when the surrounding thallus and outer capsule wall decay and decompose.

In mosses like Funaria, stomata are present exclusively on the apophysis, which is the sterile basal region of the capsule. These stomata are considered primitive because they often consist of a single ring-like guard cell with a central pore, rather than two distinct kidney-shaped guard cells.

In the liverwort Riccia, the sex organs (antheridia and archegonia) develop on the dorsal surface of the thallus and become deeply embedded within cavities of the photosynthetic tissue as the thallus grows. In mosses and ferns, the sex organs are typically superficial or borne on specialized structures rather than being embedded deep within the vegetative thallus.

Chlorenchyma is a specialized parenchymatous tissue containing chloroplasts, responsible for photosynthesis. In the sporophyte of a moss, particularly in the outer layers of the capsule wall and the apophysis region, chlorenchyma is well-developed, allowing the sporophyte to manufacture some of its own food. Chlorella is a unicellular alga, Aspergillus is a non-photosynthetic fungus, and pollen tubes lack chlorenchyma.