Pteridophytes (Tracheophytes Without Seeds)
Division Lycophyta
Order Lycopodiales
|
A club moss (Lycopodium clavatum) from Oregon. The upright stalk bears a spore-bearing, cone-like structure (strobilus) at its tip. The strobilus is composed of numerous scale-like sporophylls, each bearing sporangia in the axils. The stem and leaves are vascular, unlike true mosses. Lycopodium has only one type of spore, a condition termed homosporous. This genus is considered more primitive than the heterosporous genus Selaginella.
|
Order Selaginellales
|
Selaginella bigelovii, a common member of the division Lycophyta in dry chaparral areas of southern California. It often grows on bare ground and rock, and superficially resembles a true moss from a distance. Unlike Lycopodium, it is heterosporous with two types of spores. Right: Close-up view of the sporangia-bearing leaves (sporophylls). The upper greenish megasporangium contains 4 female megaspores. The orange microsporangia contain numerous, minute male microspores. The stem and scale-like leaves are vascular (with xylem tissue), unlike true mosses.
|
|
A low-growing, ash-colored species of Selaginella (S. cinerascens), a member of the division Lycophyta in dry, clay soils of southern California. It sometimes appears in the beds of vernal pools after they have dried up. The stem and minute scale-like leaves are vascular, unlike true mosses. The reptile in photo is a coastal horned lizard (Phrynosoma coronatum).
|
|
Selaginella densa in Grand Teton National Park, Wyoming. The upright leafy branches contain orange microsporangia in the leaf axils (white arrow).
|
|
Petrified bark of an ancient scale tree (division Lycophyta) that lived in swampy lowlands during the Pennsylvanian Period, approximately 250 million years ago. The vertical rows of leaf scars are similar to those of Sigillaria. Trees of this genus reached 100 feet (30 m) tall with a trunk diameter of 6.5 feet (2 m). Another genus of tree lycopods (Cordaites) may have included the ancestors of modern conifers.
|
Order Isoetales
|
Quillworts Isoetes orcuttii, an interesting member of the division Lycophyta in vernal pool areas of southern California. These plants superficially resemble minute onions with their narrow leaves and basal corm from which the roots arise. They do not produce flowers or seeds. Sac-like sporangia are produced in the axils of the widened leaf bases. Most of the sporangium is covered by a transparent outer membrane called the velum. Each megasporagium produces 4 female megasores. Microsporangia produce numerous small microspores (visible in right image). The leaves of I. orcuttii are generally less than 8 cm long. Isoetes nuttallii has longer leaves 8 - 20 cm in length. In another San Diego species I. howellii the velum typically covers less the 75% of the sporangium. These plants resemble little grasses in the mud and are commonly overlooked.
|
Division Sphenophyta
Order Equisetales (Horsetails)
|
Horsetails (Equisetum hyemale), a primitive vascular plant group of the Carboniferous Period (300 million years ago) with jointed stems and a terminal spore cone (strobilus). They are also called "scouring rushes" because the silica-impregnated stems were used to clean pots and pans.
|
Division Pterophyta
Order Filicales (True Ferns)
|
The sporophyte of bird's nest fern (Asplenium nidus), showing broad leaves with linear brown sori on the underside. Each sorus is composed of hundreds of sporangia forming a brown line.
|
|
Underside of the sporophyte leaf of a sword fern (Polystichum munitum) showing numerous sori (sporangia clusters). Each sorus is composed of many egg-shaped sporangia and is covered by a circular membrane called an indusium. This is NOT an infestation of scale insects.
|
|
Microscopic view of a fern sporangium (400 x). The annulus is a special hygroscopic belt of cells around the sporangium. As the sporangium dries, cells of the annulus shrink. A differential thickening of the cell walls causes the curved annulus to straighten, thus ripping apart the thin-walled lip cells and releasing the spores. Germination of a spore produces a minute heart-shaped prothallus (gametophyte).
|
|
The birth of a fern: A tiny fern sporophyte (S) emerging from a transparent, thalluslike fern gametophyte (G). Small rootlike rhizoids can be seen on the lower side of the gametophyte. The gametophyte (prothallus) develops from a spore and produces the sex cells (egg + sperm) that give rise to a fern sporophyte. Fern spores germinate and grow into a transparent gametophyte before the typical fern sporophyte appears. This is how all ferns start, including the first fern spores that ever reached the Hawaiian Islands by strong winds and air currents, long before the arrival of the first Polynesian sailors. The head of an ordinary straight pin is shown as a size relation.
|
|
Left: Bracken fern (Pteridium aquilinum) on Palomar Mountain in San Diego County, California. Signs have been placed in Palomar Mountain State Park to discourage the picking of young, uncurling fronds called fiddleheads. Right: Closeup view of immature, uncurling frond called a fiddlehead or crosier. In Asian countries, fern fiddleheads of a related species are steamed and eaten with rice as a side dish or mixed with other vegetables. Fresh fiddleheads have a pleasant buttery, nutty flavor. Considering that each fiddlehead develops into a large compound leaf, numerous people foraging for fern fiddleheads on Palomar Mountain could decimate the population of this lovely fern.
|
|
Australian tree fern (Alsophila australis) showing the uncurling frond called a fiddlehead or crosier. Smaller divisions of the compound leaf (called pinnae) also uncurl as the large leaf expands.
|
|
Mother Fern (Asplenium bulbiferum), an interesting Australian fern that produces miniature plantlets or bulblets on its leaves. The red arrow points to the tiny fiddlehead of a plantlet. Sometimes the term viviparous is used for plants that bear live young.
|
A 270 Million-Year-Old Petrified Tree Fern
During the Carboniferous Era, approximately 300 million years ago, the earth was dominated by extensive forests of giant lycopods (division Lycophyta), horsetails (division Sphenophyta) and tree ferns (division Pterophyta). Much of the earth's coal reserves originated from massive deposits of carbonized plants from this era. Petrified trunks from Brazil reveal cellular details of an extinct tree fern (Psaronius brasiliensis) that lived about 270 million years ago, before the age of dinosaurs. The petrified stem of Psaronius does not have concentric growth rings typical of conifers and dicot angiosperms. Instead, it has a central stele composed of numerous arcs that represent the vascular bundles of xylem tissue. Surrounding the stem are the bases of leaves. In life, Psaronius probably resembled the present-day Cyathea tree ferns of New Zealand.
|
A petrified trunk from the extinct tree fern Psaronius brasiliensis. The central stele region contains arc-shaped vascular bundles of xylem tissue. The stem is surrounded by leaf bases which formed the leaf crown of this fern, similar to present-day Cyathea tree ferns of New Zealand. This petrified stem has been cut and polished to make a pair of bookends.
|
|
A well-preserved stem section from the extinct tree fern Psaronius brasiliensis. Note the central stele region containing arcs of xylem tissue (vascular bundles). The structure of this stem is quite different from the concentric growth rings of conifers and dicots, and from the scattered vascular bundles of palms.
|
Order Marsileales
|
Clover-leaf Fern (Marsilea vestita), showing the characteristic compound leaves divided into 4 leaflets. This unusual aquatic fern grows in Cuyamaca Lake in San Diego County, California.
|
|
Pillworts (Pillularia americana), an interesting member of the division Pterophyta (Order Marsileales) in vernal pool areas of southern California. The simple, filiform leaves are usually less than 6 cm long. The small, pill-like structures are sporocarps that contain male microsporangia and female megasporangia. The generic name is derived from the Latin pilula (little ball), referring to the globose shape of the sporocarp. Like the quillworts (Isoetes), this plant is often overlooked because of its small, grass-like appearance.
|
Order Ophioglossales
|
Two adder's tongue ferns (Ophioglossum californicum), an interesting (and uncommon) member of the division Pterophyta (Order Ophioglossales). Each fern has a basal leaf and upright reproductive stalk. The upright stalk (spike) bears 2 rows of spore-bearing sporangia. According to Judd, et al. (Plant Systematics: A Phylogenetic Approach, 2002 page 90), Ophioglossum reticulatum has a chromosome number of 2n=1440, a record for the number of chromosomes per diploid (sporophyte) cell. Compare this number with your diploid number of 46. Photo taken in a vernal pool habitat in San Diego County, California.
|
|
Adder's tongue fern (Ophioglossum californicum), an interesting (and uncommon) member of the division Pterophyta (Order Ophioglossales). Each fern has a basal leaf and upright reproductive stalk. The upright stalk (spike) bears 2 rows of spore-bearing sporangia.
|
|
Two individual plants of adder's tongue fern (Ophioglossum californicum) which have sprouted from the same perennial caudex. The caudex was carefully removed from the ashy soil of recently burned chamise chaparral (Adenostoma fasciculatum) in a disturbed area just outside the eastern boundary of Daley Ranch north of Escondido. This area was burned during the Paradise Fire of October 2003.
|
Order Salviniales (Water Ferns)
|
Several water fern plants (Azolla filiculoides) floating on the water surface. The plant in upper right with oval fronds is a duckweed (Lemna minuta). The minute plants which resemble tiny green bubbles are Wolffia borealis and another interesting species W. columbiana, two of the world's smallest flowering plants.
|
|
The water fern (Salvinia rotundifolia), a ubiquitous floating fern in quiet waters of streams and ponds throughout tropical America, Africa and Florida. The small duckweed in photo is Landoltia punctata.
|
|
Return To The Major Divisions Of Life