Pteris or brake is a genus of close to 280-300 species of ferns widely spread across subtropical and tropical regions. They are a terrestrial genus inhabiting shady and moist forests and hilly areas. Pteris, the Latin name corresponds to 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 upto an altitude of 2400 m starting from 1200 m, P.vittata grows less than 1200 m altitudes. In India, some of its species are – P.wallichiana, P.stenophylla, P. quadriaurita, P.pellucida, P.critica, P.vittata, etc
In the life cycle of Pteris, sporophyte is the dominant phase. It can be differentiated into stem, roots and leaves. Roots are black, slender and wiry arising from the underside of the Rhizome. It can also be around the surface. The embryo gives rise to primary roots which have a short life span, they are soon replaced by the adventitious roots.
The underground stem 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 are unipinnately compound, macrophyllous, arising in an acropetal pattern on the rhizome. Pinnae’s dissections are not as low compared to Pteridium. The Bipinnate leaves, 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 eventually narrow down while reaching the apex while they are broader towards the base. The leaflets at the middle are large while other leaflets exhibit a gradual decline in the size in the apical and basal sections of the rachis. Leaflets are rough having a midrib, from here lateral veins project with a dichotomous type of branching. It exhibits an open dichotomous venation. The rate of growth is gradual and younger leaves exhibit circinate vernation.
Rhizome – It is oval and distinguished into cortex, epidermis and stele when seen through the T.S. section.
Epidermis – It is covered with thick cuticles and is single-layered with quadrangular cells.
Cortex – It is differentiated into four-five layers of sclerenchymatous hypodermis and the inner broad parenchymatous area. These regions possess leaf and root traces.
Stele – This structure varies between species. Meristeles (annulus of vascular strands) is found implanted in the ground tissue (parenchymatous in nature). Each of this meristele is a single-layered elliptical where the endodermis comprises casparian strips inside their radial walls. 1-2 layered pericycle (thin walls) is found enclosing the phloem underneath the epidermis. The xylem is located principle to the meristele, exhibiting central protoxylem encircling either sides of the metaxylem. It comprises the xylem parenchyma and tracheids. The Phloem on the other side has phloem parenchyma and sieve cells. It surrounds 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 in Pteris is through vegetative and asexual means.
Asexual reproduction – occurs through spore-formation. As it produces one type of spore only, it is homosporous.
Vegetative reproduction – reproduction occurs by eventual death and decaying of the older sections of the rhizome. As soon as the decay arrives at branching, the branch and main axis are detached growing as new plants.
Life Cycle of Pteris
Spores are produced in the coenosorus. The sporophyte is the dominant phase which is independent and diploid. Eventually, the spores develop into the prothallus via germination and proceed to the gametophytic stage (haploid). The nature of prothallus is short-lived, highly reduced and independent. With the assistance of archegonia and antheridia, it reproduces sexually. As a result, egg and spermatozoids are formed. Diploid zygote, which is the future normal sporophyte forms with the fertilization of the spermatozoa and the egg.
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.
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