Dryopteris
Dryopteris, or wood ferns, are ferns known for their adaptable nature and feathery fronds. Thriving in shaded, moist areas, they are popular for garden ornamentation due to their resilience. Dryopteris belongs to the Dryopteridaceae family, one of the largest fern genera in this family, encompassing diverse fern species.
1.0Classification of Dryopteris
2.0Structure of Dryopteris
Morphology of Dryopteris
The Dryopteris fern plant, representing the sporophytic generation, consists of roots, a rhizome, and leaves. Notably, only the leaves or fronds are visible above ground, while other organs are underground. The sporophyte features a partly horizontal and partly erect rhizome densely covered with brown, soft, broad scales and adventitious roots.
The large fronds, reaching heights of 15-50 centimeters or more, are pinnately compound and typically cluster annually on the rhizome's top, with leaf bases persisting after older leaves perish. Young leaves exhibit a characteristic coiled circinate manner, unfurling into pinnately compound leaves as they mature. The lower rachis portion is covered with brown scales known as ramenta. Older leaves are clearly distinguished into a petiole and lamina.
The primary root is short-lived, replaced by branched adventitious roots arising endogenously from the rhizome, which anchor the plant to the soil and absorb water and nutrients.
3.0Anatomy of Dryopteris
Rhizome
The rhizome's outermost layer, the epidermis, consists of rectangular cells that become sclerenchymatous as the rhizome ages, with a thick cuticle. Below the epidermis, a brown outer cortex forms a hypodermis, providing mechanical strength. The inner cortex is parenchymatous, storing starch and proteins. Tanniferous cells are present. The vascular cylinder is a dictyostele with oval or circular meristeles. Leaf traces are numerous in the inner cortex, with no definite node. Each meristele is bordered by endodermis and pericycle layers, both parenchymatous with casparian strips in the endodermis. Phloem surrounds the central xylem mass, divided into protophloem and metaphloem. Protoxylem has smaller tracheids, and metaxylem tracheids are larger and pitted.
Root
During the downward growth of the root through soil, the original epidermal layer is shed and replaced by the outermost layer of the cortex, known as the exodermis or rhizodermis. This layer is composed of thin-walled cells containing unicellular root hairs in the root hair zone. The cortex beneath the exodermis has two distinct zones:
- Parenchymatous Cortex: Adjacent to the epidermis, it consists of 5-7 layers of thin-walled, polygonal cells that store food and aid in water translocation from root hairs to the stelar region.
- Sclerenchymatous Cortex: Forming the central mechanical cylinder external to the vascular region, these cells have pitted thickenings and a polygonal shape. Devoid of cytoplasmic contents, they contribute to structural support.
The endodermis has barrel-shaped cells with starch-filled and casparian strip-lined walls. The pericycle is a single layer of thin-walled cells. Roots feature a diarch and exarch central stele with a central xylem plate containing metaxylem at the center and protoxylem at both ends. Phloem is organized into two alternating groups with xylem. There is no pith or secondary growth. Lateral roots arise from specific endodermal cells opposite the protoxylem groups.
Leaf
Leaf structure is examined separately for the pinnule and petiole. In the pinnule, a vertical section displays two parenchymatous epidermal layers with chloroplasts, and stomata may appear on either or both sides. The petiole's transverse section, nearly semi-circular, reveals an outer epidermis with scales, followed by a wholly sclerenchymatous hypodermis forming a mechanical cylinder for bending resistance. The remaining ground tissue is parenchymatous.
4.0Reproduction in Dryopteris
Reproduction is affected by vegetative means as well as by the formation of spores, which are produced within sac-like structures called the sporangia. The sporangia are grouped into definite structures called the sori (singular sorus). The sori are borne on the ventral surface of the pinnules which are called the sporophylls.
Vegetative reproduction
It is affected by two methods:
1. by fragmentation
2. formation of adventitious buds on the petioles
Reproduction by spores
Mature leaves carry sporangia on the lower surface of fertile leaflets. Typically, entire fronds produced during this period serve as sporophylls, with no distinction between fertile and sterile leaves. These leaves can perform both reproductive and photosynthetic functions.
5.0Structure of Sporangium
In Dryopteris, sori are arranged in two rows on either side of the median vein of a leaflet, between the margin and midrib. Each sorus is covered by a kidney-shaped indusium, originating at the base and forming an umbrella-shaped structure over the sorus. The sorus center has a placental tissue giving rise to sporangia in a mixed order. The sporangium has a stalk with three rows of cells and a water gland. The capsule is oval, resembling a biconvex lens, enclosing 48 bilateral and monolete spores. The sporangial wall is thin, flattened, and transparent, while a row of specially thickened cells called the annulus surrounds the capsule, forming an incomplete ring and a stomium at the base. Under suitable conditions each spore germinate and produce a prothallus that bears sex organs.
Gametophyte
The prothallus in Dryopteris is monoecious, featuring both male (antheridia) and female (archegonia) sex organs on the ventral side. Antheridia emerge among the rhizoids at the prothallus's posterior, while archegonia develop centrally behind the apical notch. The ventral position allows direct exposure of sex organs to moist air and water, crucial for their development and dehiscence. The prothalli are protandrous, promoting cross-fertilization.
Antheridium
The antheridia in Dryopteris are small, globular, and sessile structures. Comprising three tabular cells, namely the first ring cell, second ring cell, and cap cell, the latter acts as a lid during dehiscence, allowing the release of about thirty-two spermatozoids. The second ring cell forms the middle wall portion, encircling the antheridium, while the first ring cell extends around its basal part. Additionally, there's a fourth basal cell, serving as a single-celled stalk. The antheridial wall encloses 32 antherozoids.
Archegonium
Each archegonium that projects from the lower surface of the prothallus is a flask shaped organ. It consists of a swollen base, the venter and a projecting short slender neck. The venter is sunk in the tissue of the prothallus. The neck cells enclose a central neck canal.
Fertilization
Fertilization in Dryopteris occurs in the presence of water between the prothallus's lower surface and the soil. Fusion of male and female nuclei results in a fertilized egg that secretes a protective wall, forming a zygote or oospore. Zygote develops into embryo and further development gives rise to young sporophyte.
6.0Life cycle of Dryopteris
Common species of Dryopteris
Several common species of Dryopteris, along with their common names, include:
- Dryopteris filix-mas: Commonly known as the Male Ferns.
- Dryopteris marginalis: Often referred to as the Marginal Wood Ferns.
- Dryopteris erythrosora: Known as the Autumn Fern.
- Dryopteris wallichiana, commonly known as Wallich's Wood Ferns.