Pteris
Pteris, commonly known as brake, is a genus of ferns consisting of around 280 to 300 species. These species are found in subtropical and tropical regions, and typically inhabit shady and moist forests, as well as hilly areas. The Latin name for the genus, Pteris, is derived from the Greek word for fern.
Species of Pteris can be seen on the valleys and roadsides of North-Western and Western Himalayas. While P.cretica can grow up to an altitude of 2400 m starting from 1200 m, P.vittata grows at altitudes less than 1200 m. In India, some of its species are: P.wallichiana, P.stenophylla, P.quadriaurita, P.pellucida, P.critica, P.vittata, etc.
Classification
Kingdom: Plantae
Class: Polypodiopsida
Order: Polypodiales
Family: Pteridaceae
Genus: Pteris
Sporophyte
External Morphology
The sporophyte phase is the dominant stage in the life cycle of Pteris. It is composed of stems, roots and leaves. The roots are black, slender and wiry and arise from the underside of the Rhizome. They can also be found around the surface. The embryo gives rise to the primary roots, which have a short life span and are soon replaced by adventitious roots.
The underground stem of some species is branched and perennial, rhizomatous and surrounded with brown scales. A few of the species display lasting leaf bases on their rhizomes. Leaves arise from the upper portion of the rhizome having a long rachis. The Petiole base is sometimes covered with brown scales and other times with ramenta.
Leaves of many species can be unipinnately compound, macrophyllous, and arise in an acropetal pattern on the rhizome. Pinnae dissections are not as low compared to Pteridium. Bipinnate, digitate and decompound leaves are also observed in some species. Leaves that are developed are referred to as fronds. The rachis comprises many sessile, coriaceous, lanceolate leaflets organized in pairs except for the terminal leaflet.
The leaflets narrow towards the apex and broaden towards the base. The leaflets in the middle are larger, while the other leaflets show a gradual decrease in size from the apical to the basal sections of the rachis. The leaflets are rough with a midrib, from which lateral veins extend in a dichotomous pattern, exhibiting an open dichotomous venation. The rate of growth is gradual and the younger leaves show circinate vernation.
Anatomy
Rhizome - When viewed through a T.S. section, it is oval and can be distinguished into cortex, epidermis, and stele.
Epidermis - It is covered with thick cuticles and is composed of a single layer of quadrangular cells.
Cortex - It consists of four to five layers of sclerenchymatous hypodermis and an inner broad parenchymatous area. These regions contain leaf and root traces.
Stele – This structure varies between species, but generally consists of a meristele (annulus of vascular strands) implanted in the ground tissue (parenchymatous in nature). Each meristele is a single-layered elliptical, with the endodermis comprising casparian strips inside its radial walls. A 1-2 layered pericycle (thin walls) encloses the phloem underneath the epidermis, while the xylem is located principle to the meristele, exhibiting central protoxylem encircling either side of the metaxylem. It comprises xylem parenchyma and tracheids, while the phloem on the other side has phloem parenchyma and sieve cells, surrounding the xylem completely.
Leaflet Anatomy
The leaflet comprises mesophyll, epidermis and the vascular bundle. Epidermis is single-layered found on lower and upper surfaces. It is only the lower epidermis that has stomata. The mesophyll can be distinguished into the lower spongy spaces and upper palisade or homogenous. Sclerenchymatous strips are found both in adaxial and abaxial sides in the hypodermal regions of the midrib. The midrib has an amphicribral vascular bundle that is concentric and encircling a single layer of pericycle and the endodermis. Vascular strands are implanted in the mesophyll.
Reproduction
Reproduction in Pteris occurs through both vegetative and asexual means.
Asexual reproduction occurs through spore-formation, and as it produces one type of spore only, it is homosporous.
Vegetative reproduction occurs when the older sections of the rhizome decay and eventually die, leading to branching and the detachment of the branch and main axis, which then grow as new plants.
Life Cycle of Pteris
Spores produced in the coenosorus develop into the prothallus via germination, resulting in a short-lived, highly reduced, and independent organism. This prothallus then reproduces sexually with the assistance of archegonia and antheridia, forming egg and spermatozoa. Upon fertilization of the spermatozoa and the egg, a diploid zygote forms, which is the future normal sporophyte. The sporophyte is the dominant phase, which is independent and diploid.
Consequently, the life cycle is diplohaplontic. Since alternation of generations is seen, as there is a difference morphologically in both the sporophyte and gametophyte, they are heteromorphic.
