Gymnosperms

Gymnospermae -- from the Greek gymnos (naked) and sperma (seed) -- are seed-bearing plants whose seeds are not enclosed within a fruit, unlike those of flowering plants. Worldwide there are roughly 70 to 80 genera and around 1,000 living species; India itself is home to a modest but distinctive set of native and cultivated genera, including Cycas, Pinus, Cedrus, Ephedra and Gnetum.

General habit. Most gymnosperms are evergreen shrubs or woody trees. They represent a comparatively primitive lineage of seed plants, and their seeds sit exposed, typically on the surface of a scale-like structure gathered into a cone.

Vascular tissue. Gymnosperms are true vascular plants: their xylem is made predominantly of tracheids (vessels are generally absent, except in a few unusual genera such as Gnetum), and their phloem is made of sieve cells without companion cells.

Plant body -- root. The sporophyte plant body is differentiated into root, stem and leaves. The root system is typically of the tap-root type. In several gymnosperms the roots form symbiotic partnerships with other organisms: in Cycas, specialised coralloid roots associate with nitrogen-fixing blue-green algae (cyanobacteria); in Pinus, the roots associate with mycorrhizal fungi that assist mineral uptake.

Plant body -- stem. The stem is generally erect, aerial and solid, and it shows secondary growth because a vascular cambium is present between the xylem and phloem -- this is what allows a conifer trunk to steadily thicken with age. In Cycas the stem is usually unbranched and columnar, whereas in most conifers, such as Pinus, the stem is repeatedly branched.

Plant body -- leaves. Leaves are dimorphic, meaning two distinct kinds occur on the same plant: green, photosynthetic foliage leaves, which may be simple and needle-like (as in Pinus) or large and pinnately compound (as in Cycas); and small, brown, membranous scale leaves.

Reproductive structures. Gymnosperms are heterosporous, producing two kinds of spores on two kinds of specialised leaf-like structures. Microsporophylls, gathered into male cones, bear microsporangia that produce microspores (which develop into pollen). Megasporophylls, gathered into female cones (or, in Cycas, borne more loosely), bear megasporangia containing ovules that produce megaspores. Fertilisation in gymnosperms typically occurs through a pollen tube (siphonogamy), rather than through motile antherozoids swimming through free water, which frees the group from the strict water-dependence still seen in bryophytes and most pteridophytes. …