Plant Diversity I

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alternation of generations

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A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.

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angiosperm

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A flowering plant, which forms seeds inside a protective chamber called an ovary.

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antheridium (pl., antheridia)

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In plants, the male gametangium, a moist chamber in which gametes develop.

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apical meristem

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Embryonic plant tissue in the tips of roots and the buds of shoots. The dividing cells of an apical meristem enable the plant to grow in length.

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archegonium (pl., archegonia)

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In plants, the female gametangium, a moist chamber in which gametes develop.

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bryophyte

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An informal name for a moss, liverwort, or hornwort; a nonvascular plant that lives on land but lacks some of the terrestrial adaptations of vascular plants.

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cuticle

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A waxy covering on the surface of stems and leaves that acts as an adaptation that prevents desiccation in terrestrial plants.

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embryophyte

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Alternate name for land plants that refers to their shared derived trait of multicellular, dependent embryos.

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evolution

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Descent with modification; the idea that living species are descendants of ancestral species that were different from the present-day ones; also defined more narrowly as the change in the genetic composition of a population from generation to generation.

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foot

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The portion of a bryophyte sporophyte that gathers sugars, amino acids, water, and minerals from the parent gametophyte via transfer cells.

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gametangium (pl., gametangia)

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Multicellular plant structure in which gametes are formed. Female gametangia are called archegonia, and male gametangia are called antheridia.

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gametophore

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The mature gamete-producing structure of a moss gametophyte.

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gametophyte

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In organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes.

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grade

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A group of organisms that share the same level of organizational complexity or share a key adaptation.

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gymnosperm

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A vascular plant that bears naked seeds—seeds not enclosed in specialized chambers.

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heterosporous

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Referring to a plant species that has two kinds of spores: microspores, which develop into male gametophytes, and megaspores, which develop into female gametophytes.

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homosporous

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Referring to a plant species that has a single kind of spore, which typically develops into a bisexual gametophyte.

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hornwort

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A small, herbaceous nonvascular plant that is a member of the phylum Anthocerophyta.

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leaf

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The main photosynthetic organ of vascular plants.

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lignin

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A hard material embedded in the cellulose matrix of vascular plant cell walls that provides structural support in terrestrial species.

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liverwort

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A small, herbaceous nonvascular plant that is a member of the phylum Hepatophyta.

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lycophyte

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An informal name for a member of the phylum Lycophyta, which includes club mosses, spike mosses, and quillworts.

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megaphyll

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A leaf with a highly branched vascular system, characteristic of the vast majority of vascular plants.

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megaspore

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A spore from a heterosporous plant species that develops into a female gametophyte.

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microphyll

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In lycophytes, a small leaf with a single unbranched vein.

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microspore

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A spore from a heterosporous plant species that develops into a male gametophyte.

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moss

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A small, herbaceous nonvascular plant that is a member of the phylum Bryophyta.

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mycorrhiza (pl., mycorrhizae)

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A mutualistic association of plant roots and fungus.

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peat

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Extensive deposits of partially decayed organic material formed primarily from the wetland moss Sphagnum.

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peristome

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A ring of interlocking, tooth-like structures on the upper part of a moss capsule (sporangium), often specialized for gradual spore discharge.

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phloem

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Vascular plant tissue consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.

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phragmoplast

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An alignment of cytoskeletal elements and Golgi-derived vesicles that forms across the midline of a dividing plant cell.

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placental transfer cell

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A plant cell that enhances the transfer of nutrients from parent to embryo.

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Plantae

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The kingdom that consists of multicellular eukaryotes that carry out photosynthesis.

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protonema (pl., protonemata)

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A mass of green, branched, one-cell-thick filaments produced by germinating moss spores.

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pterophyte

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An informal name for a member of the phylum Pterophyta, which includes ferns, horsetails, and whisk ferns and their relatives.

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rhizoid

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A long, tubular single cell or filament of cells that anchors bryophytes to the ground. Unlike roots, rhizoids are not composed of tissues, lack specialized conducting cells, and do not play a primary role in water and mineral absorption.

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root

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An organ in vascular plants that anchors the plant and enables it to absorb water and minerals from the soil.

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seed

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An adaptation of some terrestrial plants consisting of an embryo packaged along with a store of food within a protective coat.

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seedless vascular plant

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An informal name for a plant that has vascular tissue but lacks seeds. Seedless vascular plants form a paraphyletic group that includes the phyla Lycophyta (club mosses and their relatives) and Pterophyta (ferns and their relatives).

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seta (pl., setae)

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The elongated stalk of a bryophyte sporophyte.

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sorus (pl., sori)

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A cluster of sporangia on a fern sporophyll. Sori may be arranged in various patterns, such as parallel lines or dots, which are useful in fern identification.

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sporangium (pl., sporangia)

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A multicellular organ in fungi and plants in which meiosis occurs and haploid cells develop.

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spore

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In the life cycle of a plant or alga undergoing alternation of generations, a haploid cell produced in the sporophyte by meiosis. A spore can divide by mitosis to develop into a multicellular haploid individual, the gametophyte, without fusing with another cell.

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sporocyte

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A diploid cell, also known as a spore mother cell, that undergoes meiosis and generates haploid spores.

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sporophyll

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A modified leaf that bears sporangia and hence is specialized for reproduction.

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sporophyte

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In organisms (plants and some algae) that have alternation of generations, the multicellular diploid form that results from the union of gametes. The sporophyte produces haploid spores by meiosis that develop into gametophytes.

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sporopollenin

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A durable polymer that covers exposed zygotes of charophyte algae and forms the walls of plant spores, preventing them from drying out.

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stoma (pl., stomata)

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A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant.

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strobilus (pl., strobili)

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The technical term for a cluster of sporophylls known commonly as a cone, found in most gymnosperms and some seedless vascular plants.

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tracheid

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A long, tapered water-conducting cell found in the xylem of nearly all vascular plants. Functioning tracheids are no longer living.

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vascular plant

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A plant with vascular tissue. Vascular plants include all living plant species except mosses, liverworts, and hornworts.

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vascular tissue

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Plant tissue consisting of cells joined into tubes that transport water and nutrients throughout the plant body.

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xylem

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Vascular plant tissue consisting mainly of tubular dead cells that conduct most of the water and minerals upward from the roots to the rest of the plant.