Gymnosperms

Key Characteristics  Vascular, seed bearing plants that lack flowers  “gymno” = naked, “sperm” = seed  Most features based on reproduction  Seeds and microsporangia on strobili  Pollen transferred from microsporangia to ovules  Ovules exposed (naked)  Ovules and seeds covered by sporophylls  Colder more temperate climates  Physiology similar to angiosperms  Typically evergreen, some deciduous species

Ecology of Gymnosperms  Like those of flowering plants, but narrower set of features and habitats  Pinophyta well adapted to colder climates: –Northern forests mostly pine and relatives –Southern forests mostly araucaria and relatives  Some gymnosperms lives in deserts; such as Ephedra, Welwitschia, and pinons  A few a tropical; ex. The cycads and Gnetum  Typically adapted to where free water is scarce  Sunken stomata, thick cuticle and tough hypodermis

Four Major Divisions of Gymnosperms  Ginkophyta (maidenhair tree)  Cycadophyta (cycads)  Pinophyta (conifers)  Gnetophyta (gnetophytes) 65 genera includes 720 species

Division Ginkophyta  Only one living species, Ginkgo biloba  Exclusively dioecious (separate sexes)  Flagellated sperm  Haustorial pollen tubes (do not convey sperm)  Fleshy integuments around seeds  Deciduous simple leaves  Seeds on simple seed stalks  Two types of leaves  Nearly extinct

Division Cycadophyta  ~10 genera and 100 species  Tropical and subtropical  Exclusively dioecious  Most species threatened  Flagellated sperm  Large strobili, fleshy integument  Palm-like leaves dissimilar to any other gymnosperm, persistent  Haustorial pollen tubes and flagellated sperm

Division Pinophyta  Generally called conifers or cone bearing  Largest division with greatest number of species  Most abundant trees in northern hemisphere  Oldest living plants  Have short shoots, long shoots and two types of leaves  Pine needle, occurs in clusters called fascicles  Tree completely replaces needles ~ 5 years  Evergreens  Life cycle is extended, may last up to 20 months

Division Gnetophyta  Very distinctive (bizarre) seed plants  3 genera and 71 species  Genera include –Ephedra (40 species) –Gnetum (30 species) –Welwitschia (1 species)  Leaves small and generally non-photosynthetic  Dioecious  Tropical only  Use pollen tube for transport of sperm  Double fertilization (only ones among gymnosperms)

Economic Importance  In northern hemisphere = use of wood for making paper and lumber  Resins, rosins, turpentine and amber