School of Sciences, Lautoka Campus BIO509 Botany Lecture 14: Phylum Polypodiophyta (ferns)

Phylum Polypodiophyta (ferns)

Some 11,000 species. largest group of plants beside flowering plants. Relatively abundant in fossil record. Most diverse & most abundant in the tropics. About 30% of tropical ferns are epiphytic. No secondary growth (wood formation). Have megaphylls (system of veins – venation) commonly referred to as fronds. Most ferns are homosporus. Water ferns are the only heterosporous living ferns. Require water for sexual reproduction. Various forms from tiny floating forms to giant tree ferns.

Some ferns of Fiji

Tree ferns (balabala) Cyathea lunulata To 24m high and stems to 30cm in diameter. Thickening of stem is accomplished by deposition of fibrous root material.

Botrychium Herbaceous 1 sp. in Fiji (Nadarivatu) Only living fern genus with vascular cambium (produces secondary growth- wood)

Bird’s nest fern Asplenium nidus Epiphytic. Debris collects in the nest and gradually turns into humus.

Pyrrosia Epiphytic ferns. Rhizomes are exposed to air.

Basket fern Drynaria rigidula Form a basket to catch the rain and falling detritus from higher up in the rainforest canopy from which fertile fronds grow.

Vegetable fern – Ota Diplanzium proliferum Most commonly consumed fern

Golden leather fern Acrostichum aureum Common species in brackish swamps throughout Fiji. Thick leathery leaves. Young fronds are edible when boiled.

Floating ferns Salvinia Water fern Leaves in whorls of 3: two float and are covered by hairs, other hangs down, divided so looks root-like and bears sporangia. Heterosporus Salvinia auriculata: introduced to Fiji for aquaria, has escaped and is now established along rivers.

Water fern Marsilea Leaves like clover Slender rhizomes Grow in mud / damp soil, often with leaves floating on water surface. Produce drought-resistant sporocarps (bean-shaped reproductive structures) Germinate in water to produce megasporangia and microsporangia

Fern Reproduction The sporophyte is the dominant or conspicuous phase of the life cycle. Sporophyte consist of fronds, rhizome (stem), adventitious roots and ‘fiddleheads’. Blades are divided into segments called pinnae (singular: pinna) that are attached to a midrib or rachis. When blades mature, small circular rust-colored patches (clusters) appear on the lower surface. These are sporangia. These clusters are called sori (singular: sorus)

Fronds first tightly coiled (fiddleheads) leaf development known as circinate vernation Uncoil due to differential growth on top and bottom.

Expanded mature fronds have small circular rust colored sporangia Expanded mature fronds have small circular rust colored sporangia. Sporangia occur in numerous clusters called sori (singular sorus). Sori are protected by indusia (singular –indusium).

Microscopic sporangia are surrounded by a row of brownish cells which look like tiny millipede called the annulus. Annulus helps in dispersing the spores. Under the influence of moisture, catapults spores out.

Gametophytes Spores germinate in moist habitats Grow into gametophyte (prothallus; 5-6 mm) Antheridia produce flagellated sperm. Fertilization occur on archaegonia Single zygote forms Grows into sporophyte Gametophyte disintegrates.

Human and Ecological Relevance of Ferns Ferns make ideal house plants (require low light, not susceptible to pests) Ferns act as air filters removing air pollutants Tree ferns provide good shade for anthuriums. Ferns are eaten in many parts of the world. Has been used in folk medicine. Fronds can be used for thatching houses.

Questions??