Systematic Position
Kingdom: Plantae
Subkingdom: Tracheobionta
Division: Pteridophyta
Class: Filicopsida
Order: Polypodiales
Family: Pteridaceae
Genus: Pteris L.
Interesting Science Videos
Habit and Habitat of Pteris (Brake Fern)
Pteris is represented by about 300 species that grow abundantly in the tropical and sub-tropical regions of the world. They are either terrestrial or lithophyte and usually are distributed at lower altitudes.
Morphology of Pteris (Brake Fern)
The roots of Pteris are black, and slender and arise from the rhizome. The primary root is short-lived which is later replaced by adventitious roots.
The plants have creeping rhizomes in P. biaurita, P. vittata, and P. glandiflora. In P. cretica, the rhizome is branched, short, stumpy, and semi-erect. The rhizome is covered with scales. Hairs are absent. Roots arise from the lower surface of the rhizome.
The leaves are pinnately compound, microphyllous, rarely digitate. The petioles are covered with scale. Venation is of open furcate type. The leaves in P. vittata are uni-pinnate whereas the leaves of P. biaurita are bi-pinnate. In P. vittata, the pinnae are smaller near the base, large near the middle, and decreasing in length towards the apex to look spindle-shaped.
The leaf apex is occupied by an old leaflet or pinna. Every pinna is traversed by a central midrib which gives off lateral veins that bifurcate near the tip. The pinnae are sessile and are broad at the base and gradually taper towards the apex.
Anatomy of Pteris (Brake Fern)
Rhizome– The transverse section of the rhizome reveals the following layers-
Epidermis– It is the outermost layer made up of quadrangular cells which are cuticularized.
Cortex or ground tissue– It is differentiated into the sclerenchymatous hypodermis and parenchymatous layer.
Endodermis and pericycle– A single-layered endodermis is found beneath the cortex which comprises Casparian strips. Beneath the endodermis lies one or two layered pericycle that enclose the stele.
Stele– Beneath the pericycle lies the stele and this varies from species to species. It is solenostelic in P. glandiflora and P. vittata, a simple dictyostelic in P. cretica and younger regions of P. vittata. In the younger branches of rhizome in P. biaurita, the stele is mixed protostele in the lower region. It becomes siphonostelic a little higher and solenostelic at the apex.
Pinnules or leaflet– The anatomy of pinnules reveals the following layers-
The pinnule has upper and lower epidermal layers. In P. cretica, the upper epidermis has larger cells with less sinuous walls. The stomata are restricted to the lower epidermis which has smaller cells and more sinuous walls. The mesophyll may or may not be differentiated into palisade parenchyma and spongy parenchyma. The midrib region has a single concentric type of vascular strand with distinct endodermis. The bundle sheath extensions are prominent and occur as groups of thick-walled cells below the upper and above the lower epidermis. Palisade and spongy tissue are absent around the mid-rib.
Petiole–
The petiole is traversed by a single C-shaped, U-shaped, or V-shaped leaf trace. In P. biaurita, the U-shaped leaf trace enters the petiole and becomes V-shaped higher up. The xylem has two adaxial hooks. In the rachis, the petiole trace gives off strands into its pinnae if the leaf is unipinnate or it divides to give rise to secondary and tertiary pinna traces in bipinnate leaves. The rachis traces are marginal in origin and are usually flat U-shaped, or shallow arc-like.
Reproduction in Pteris (Brake Fern)
Pteris reproduces through vegetative, asexual, and sexual means-
Vegetative reproduction
It occurs by the death and decay of older parts of the rhizome. The young parts of the rhizome separate and give rise to new individuals.
Sporophyte
Pteris reproduces asexually by the formation of spores.
Sorus– The sorus is of continuous type (Coenosorus) and is protected by the upper indusial flap that is formed by the margins of the pinnae. The receptacle is intramarginal in origin. Sori are of mixed type i.e. they are intermingled with many multicellular linear hairs present on the ventral surface of the leaf.
Development of sporangium– In Pteris, the sporangium development begins with a single superficial cell called the sporangial initial, which undergoes transverse division to form an upper and a lower cell.
The upper cell further divides by oblique walls, creating an apical cell with three cutting faces.
This apical cell produces two segments and divides periclinally to give rise to the outer jacket initial and an inner tetrahedral archesporial cell.
The archesporial cell then divides to form the tapetal initial and a primary sporogenous cell. The tapetal initial proliferates into the tapetum layers by several anticlinal and periclinal divisions, while the primary sporogenous cell divides to form spore mother cells, which subsequently undergo meiosis to produce four haploid spores.
The tapetum provides nourishment to the developing spores, whereas the lower cell does not contribute to sporangium formation.
A mature sporangium in Pteris features a long stalk and a capsule.
The capsule’s single-layered jacket consists of three types of cells: large parenchymatous cells with undulated walls, radially arranged thin-walled stomium, and a thick-walled vertical annulus that partly encircles the sporangium.
Spore–Pteris is homosporous, producing spores that are similar in structure and function.
The spores are bluntly triangular with a distinct tri-radiate mark, and the thick spore wall comprises an exine and intine. The exine is variously sculptured, and spore dispersal occurs through the air due to the shrinkage of cells in the annular region, causing dehiscence along the stomium.
Gametophyte
The germination process in the Pteris begins when the spore wall (exine) ruptures, allowing the inner contents to emerge. These contents undergo transverse division, forming a prothallial cell and a rhizoid initial. The prothallial cell further divides to produce an apical terminal cell and a small filament. The apical terminal cell continues to divide, eventually developing into a mature, heart-shaped (cordate) prothallus, which is capable of photosynthesis.
Rhizoids, which help anchor the prothallus, develop on its ventral surface, and growth occurs from an apical notch.
Typically, Pteris prothalli are monoecious and exhibit protandry, meaning the male reproductive organs (antheridia) develop before the female ones (archegonia).
Antheridia: The antheridia are located on the ventral side of the prothallus and originate from a superficial cell. This cell divides transversely into an upper and a lower cell (first ring cell), with the upper cell undergoing periclinal division to form a dome-shaped cell and a primary androgonial cell.
The dome-shaped cell divides transversely to produce a cover cell and a second ring cell. Both cover and ring cells divide anticlinally, creating a single-layered jacket around the antheridium. The primary androgonial cell undergoes repeated divisions, forming androcytes, which then transform into antherozoids.
Archegonia: The archegonium is a flask-shaped structure that arises from a superficial cell on the prothallus, known as the archegonial initial. This initial cell divides periclinally to form an outer primary neck cell (primary cover cell) and an inner cell.
The inner cell further divides into an upper central cell and a lower basal cell, while the outer primary neck cell undergoes two anticlinal divisions to create neck cells. The central cell divides into an outer primary neck canal cell and an inner primary venter cell. The primary neck canal cell forms neck canal cells, and the primary ventral canal cell divides to produce an upper ventral canal cell and a lower egg cell.
Fertilization in Pteris (Brake Fern)
During fertilization, the antheridium absorbs water and swells, causing the cover cells to split and release antherozoids in the presence of water. Simultaneously, the ventral canal cell of the archegonium disorganizes, producing mucilage that forms an open passage for the antherozoids. The antherozoids swim towards the egg and fuse with it to form a zygote.
Embryo Development
The zygote undergoes vertical and transverse divisions, reaching a quadrant stage and eventually forming a 32-celled stage. Cell differentiation begins at this stage. In Pteris, the hypobasal cells give rise to the stem apex and foot, while the epibasal cells develop into the root and cotyledons. Formation of the suspensor does not take place. The venter of the archegonium forms a calyptra around the developing embryo, leading to the emergence of a new plant.
Economic Importance of Pteris (Brake Fern)
Pteris multifida is used for its anti-inflammatory properties in China. Pteris biaurita is applied on cuts and wounds. Different other species are used to treat skin diseases, respiratory issues, and digestive disorders. Pteris species have been studied for their antioxidant and antimicrobial properties.
Pteris vittata, also known as Chinese brake fern is used as ornamental plants because of its aesthetic appeal and is globally recognized for its ability to hyper-accumulate arsenic from contaminated soils.
The rhizome of Pteris is rich in starch and is used as food. Fronds are used as a fuel and thatching material for cottages. Pteris was used as a source of potash for soap and glass making during the 10th century.
Pteris ferns are also significant in scientific research, particularly in the study of plant genetics and evolutionary biology. Their unique reproductive strategies and adaptability to different environments make them an interesting subject for botanists and ecologists worldwide.
Pteris cretica and Pteris multifida, are used as bio-indicators in environmental monitoring. Their sensitivity to air pollutants, such as sulfur dioxide and heavy metals, allows scientists to assess the health of ecosystems and the extent of pollution in urban and industrial areas.
References
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- Ojha,Rijan., Devkota, Hari,Prasad., 2021. Edible and Medicinal pteridophytes of Nepal: A review.Ethnobotanical Research and Applications. 22:16. http://dx.doi.org/10.32859/era.22.16.1-6
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