Life on Earth Kingdom Plantae Part III “Ferns” Boston fern

Two Life Cycle Stages of Ferns GAMETOPHYTE SPOROPHYTE Pteridium (bracken fern)

Phylum: Moniliophyta Subphylum: Pterophyta (typical ferns, including water ferns, tree ferns, and grape ferns) Subphylum: Psilophyta (wisk ferns or psilophytes) Subphylum: Sphenophyta (horsetails and scouring rushes)

Subphylum: Pteridophyta (“typical ferns”) Plants with megaphyllous leaves (called fronds) with branched veins Most species have no “stem” but a perennial rhizome All species are homosporous except the “water ferns” Some species produce dimorphic fronds (vegetative and reproductive fronds)

Fern Terminology Pinna Rachis

Osmunda (fertile and sterile fronds)

Frond Development Fronds develop in a coiled fashion known as circinate vernation Young, coiled fronds are called fiddleheads Some ferns are edible at this stage

Fern Reproduction Fern plants ( diploid sporophytes) produce spores by meiosis in sporangia These sporangia develop in small clusters (called sori) on the underside of the pinnae (or on separate pinnae) Some species produce a protective indusium partially covering the sorus

Fern Sporangia

Pinna with Sori (no indusium) sorus

Fern Sori with Indusia

Frond with Sori and Indusia

Fern Sporangia with Annulus Sporangia forcibly eject the spores with the action of the annulus and lip cells

Gametophyte Generation Spores develop by mitosis into haploid, photosynthetic gametophytes The gametophyte thallus usually produces male antheridia first, then female archegonia Flagellated sperm fertilize egg cells and the zygote develops into the next sporophyte fern plant

Gametophyte Generation

Fern Antheridia

Young Sporophytes

Fern Life Cycle

Fern Diversity Some tropical species are “tree ferns” and produce a erect stem (especially the Order Marattiales) Many ferns are epiphytes Some ferns are aquatic (floating) These “water ferns” are heterosporous, while all other ferns are homosporous Ferns are important economically as ornamentals

Platycerium

Pleopeltis polypoides “resurrection fern”

Water Ferns (Azolla)

Azolla from a Distance

Marsilea (another water fern)

Marsilea

Salvinia and Azolla

Tropical Tree Ferns (Marattiales)

Tree Fern

Tree Fern

Grape Ferns Ophioglossum and Botrychium

Botrychium

Subphylum: Psilophyta (wisk ferns) Extant plants superficially similar to rhyniophytes, but now known to be “reduced” ferns No true roots or leaves; homosporous Erect “stem” and underground “rhizome” have protostele structure Dichotomous branching common

Psilotum Psilotum (“wisk fern”) produces trilobed sporangia on flaps of tissue called enations previously viewed as a separate division, the Psilophyta

Psilotum

Tmesipteris (another Psilophyte from SE Asia and New Zealand)

Subphylum: Sphenophyta Includes “horsetails” and “scouring rushes” Only one extant genus: Equisteum Characteristics: hollow, jointed stems microphyllous-like leaves homosporous

Equisetum

Sheathing Leaves and Plants with Strobili

Equisetum (strobilus)

Equisetum (cont.) spores with two wall layers outer wall is hygroscopic and humidity changes cause unwrapping of the 4 arms (elaters) this action helps to break up the spore mass in spore dispersal

Equisetum spores and elaters