Gymnosperms and Conifers

Gymnosperms Introduction

• The oldest identified seeds are from the Late Devonian period, dating back over 350 million years.
• Seeds provide land plants with key adaptations like a protective seed coat, food supply for the embryo, and dormancy during unfavorable conditions.
• The first seed plants, originally fern-like pteridosperms or seed ferns, are now classified as gymnosperms.
• Gymnosperm means "naked seed", referring to how seeds are produced on the surface of sporophylls.
• Pollen cones facilitate pollen grain production, whereas female gametophytes grow inside ovules.

Pinophyta (Conifers)

• Pinophyta includes pines, firs, spruces, and cedars
• Conifer fossils' age can be traced back to the late Carboniferous period (290 million years ago).
• Conifers have needle-like leaves arranged in clusters called fascicles.
• Conifers have adaptations to harsh conditions: thick cuticle, sunken stomata, and resin canals.
• Conifer wood is softwood, and consisting entirely of tracheids.

Ginkgophyta (Ginkgo)

• Ginkgo biloba is the only living representative of Ginkgophyta.
• Ginkgos have fan-shaped leaves.
• Ginkgo seeds are enclosed in a fleshy covering.

Cycadophyte (Cycads)

• Cycads have palm-like leaves.
• Cycad life cycles are similar to conifers.
• Cycads are dioecious, having separate male and female plants.

Gnetophyta

• Gnetophyta includes three genera: Ephedra, Gentium, and Welwitschia.
• Gnetophytes have vessels in the xylem.
• Ephedra are shrubby plants found in dry regions.
• Gnetum are vine-like plants, which have large leaves and are found in the tropics.
• Welwitschia is restricted to the deserts of southwestern Africa and has only two strap-like leaves.

Human Relevance of Gymnosperms

• Conifers have edible inner bark and seeds.
• Conifers are used for masts in sailing vessels, crates, boxes, furniture, telephone poles, railroad ties, and mine timbers.
• Conifers are sources of turpentine and rosin
• Conifers are used for fuel, pulpwood, construction lumber, and ornamentals.
• Taxol, a pharmaceutical, is derived from yew trees.
• Ginkgo seeds are edible after removing the seed coat.
• Ginkgo extracts are thought to increase blood circulation.
• Ephedra (Mormon tea) contains ephedrine, which is used for respiratory problems.

Seedless Vascular Plants Introduction

• Internal conducting tissue developed during early vascular plant evolution.
• True leaves appeared during early vascular plant evolution.
• Roots developed for absorption and anchorage during early vascular plant evolution.
• Gametophytes became progressively smaller during early vascular plant evolution.
• Seedless vascular plants include four phyla: Psilotophyta, Lycophyta, Equisetophyta, and Polypodiophyta.

Psilotophyta (Whisk Ferns)

• Sporophytes lack true leaves and roots.
• Stems and rhizomes fork evenly (dichotomously).
• Enations (tiny, green, veinless flaps of tissue) grow along stems.
• Mycorrhizal fungi aid roots which are scattered along rhizomes.

Lycophyta (Ground Pines, Spike Mosses, and Quillworts)

• Lycophytes have plants covered with microphylls (leaves with a single vein).
• Lycopodium (Ground Pines) have stems that develop from branching rhizomes, with sporangia in the axils of sporophylls.
• Selaginella (Spike Mosses) are abundant in the tropics, with leaves having a ligule on the upper surface.
• Isoetes (Quillworts) are found in areas partially submerged in water, and their microphylls are arranged in a tight spiral.

Equisetophyta (Horsetails and Scouring Rushes)

• Sporophytes have ribbed stems containing silica.
• Whorled, scale-like microphylls lack chlorophyll
• Equisetum can be branched and unbranched forms with jointed stems.
• Stomata are located in grooves between ribs.
• Hollow central cavity, carinal canals, and vallecular canals are present in stem anatomy.

Polypodiophyta (Ferns)

• Sporophytes have megaphylls (leaves with more than one vein) that are often large and divided.
• Fern leaves are fronds, which are typically divided into smaller segments.
• Ferns require external water for reproduction.
• Fronds first appear coiled in a crozier (fiddlehead).
• Sporangia may be scattered on the lower leaf surface or found in discrete clusters called sori, protected by indusia.

Human and Ecological Relevance for Ferns

• Ferns are used as houseplants and outdoor ornamentals.
• Rhizomes are cooked as food.
• Used in folk medicine and for thatching houses.
• Used in basketry and weaving.

Bryophytes Introduction

• Developed features reduce drying: fatty cuticle to retard water loss, multicellular gametangia/sporangia surrounded by a jacket of sterile cells, and zygotes developed into multicellular embryos within parental tissues.
• Bryophytes include about 23,000 species of mosses, liverworts, and hornworts.
• Bryophytes can occupy a wide range of habitats, from damp banks to bare rocks and frozen alpine slopes.
• Bryophytes often have mycorrhizal fungi associated with their rhizoids.
• Peat mosses are ecologically important in bogs.
• Luminous mosses are found in caves and other dark, damp places.
• Bryophytes lack true xylem or phloem
• Bryophytes need require external water for sexual reproduction.

Hepaticophyta (Liverworts)

• Most common liverworts have flattened, lobed thalli.
• Thalloid liverworts make up about 20% of species, while 80% are leafy.
• Thalli or leafy gametophytes develop from spores, which may produce protonema.
• Marchantia form gametangia on gametophores (antheridiophores and archegoniophores).
• Riccia is one of the simplest liverworts, with a sporophyte of solely a spherical capsule.

Bryophyta (Mosses)

• There are about 15,000 species of mosses.
• Mosses are divided into three classes: peat mosses, true mosses, and rock mosses.
• Leaves of moss gametophytes are one-cell thick, except at the midrib.
• Mosses have an axis stem-like, without xylem or phloem.
• Gametangia are present at apices of leafy shoots (archegonia and antheridia).
• A mature sporophyte consists of a capsule, seta, and foot.

Anthocerophyta (Hornworts)

• Mature sporophytes look like miniature greenish-blackish rods.
• Gametophytes are thalloid with one large chloroplast per cell.
• Thalli have pores and cavities filled with mucilage containing nitrogen-fixing bacteria.
• Hornworts have a sporophyte with numerous stomata and a meristem that continually increases its length.

Human and Ecological Relevance for Bryophytes

• Pioneer species on bare rock, contributing to succession.
• Retain moisture and reduce flooding and erosion.
• Act as indicators of surface water.
• Used as packing material.
• Peat mosses are used as soil conditioners, poultice material, and fuel.

Plant Names and Classification Introduction

• All living organisms are given a two-word Latin scientific name.
• A Latin name uniquely identifies a species.
• There is one correct scientific name per species.
• Many common names may exist for the same species.

Development of the Binomial System of Nomenclature

• Theophrastus made the first attempt to classify plants in the 4th century B.C.
• Carolus Linnaeus (1707–1778) established the Binomial System of Nomenclature.
• Linnaeus published Species Plantarum in 1753.
• Latin phrases were changed to reflect relationships, placing species in genera.

The International Code of Botanical Nomenclature

• The International Code of Botanical Nomenclature standardizes rules for naming and classifying plants.
• Linnaeus is the starting point for names.
• Rules are revised at international botanical congresses.
• Requires a Latin description of the plant and a designated type specimen in a herbarium.

Classification of Major Groups

• Genera are grouped into families.
• Families are grouped into orders.
• Orders are grouped into classes.
• Classes are grouped into phyla (divisions).
• Phyla are grouped into kingdoms.
• Example: Onion
  • Kingdom: Plantae
  • Phylum: Magnoliophyta
  • Class: Liliopsida
  • Order: Liliales
  • Family: Liliaceae
  • Genus: Allium
  • Species: Allium cepa L.

The Species Concept

• Morphological Species Concept: Defined by morphology.
• Interbreeding Species Concept: Capable of interbreeding and reproductively isolated from other groups.
• Ecological Species Concept: Occupies a unique ecological niche.
• Eclectic Species Concept: Uses morphological, geographical, biological, and ecological criteria.
• Nominalistic Species Concept: Species do not exist; the evolutionary unit is a local interbreeding population.

Terms - Bryophytes

• Hydroid: Water-conducting cells in mosses.
• Leptoid: Food-conducting cells in mosses.
• Thalli: Flattened, lobed structures in liverworts.
• Protonema: Immature gametophyte consisting of short filaments.
• Antheridia: Male gametangia.
• Archegonia: Female gametangia.
• Paraphyses: Sterile filaments among gametangia.
• Calyptra: Cap on top of the moss sporophyte.
• Peristome: Teeth under the operculum at the tip of the capsule in mosses.
• Operculum: A lid or flap covering the peristome of a moss capsule.

Terms - Ferns

• Megaphyll: Leaves with more than one vein.
• Enation: Tiny, green, veinless flaps of tissue.
• Sporophyll: Sporangium-bearing leaves.
• Strobili: Cone-like structures bearing sporangia.
• Carinal Canal: Canals conducting water in horsetail stems.
• Vallecular Canal: Air-filled canals in horsetail stems.
• Elator: Aids in spore dispersal in horsetails.
• Frond: Fern leaf.
• Crozier: Fiddlehead; coiled young fern leaf.
• Pinna: Segment of a fern frond.
• Sori: Clusters of sporangia on fern leaves.
• Indusium: Protective covering over a sorus.
• Annulus: Row of heavy-walled cells that catapult spores out of the sporangium.
• Prothalli: Fern gametophytes.

Terms - Gymnosperms

• Integument: Protective layer around the megasporangium.
• Fascicle: Cluster of needle-like leaves in pines.
• Hypodermis: Layer below the epidermis.
• Resin: Antiseptic and aromatic substance in resin canals.
• Softwood: Conifer wood consisting of tracheids.
• Hardwood: Broadleaf tree wood with vessels and fibers.
• Micropyle: Pore in the integument of an ovule.