page_title: Glossary of botanical terms
section_title: T
hierarchical_section_title: Glossary of botanical terms / T
caption_attribution_description: Cucurbita pepo
context_page_description: This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology.
context_section_description: taproot
  The primary descending root of a plant with a single dominant root axis.
  tartareous
  Having a surface that is course, thick, rough, and crumbling.
  taxon 
   
  A group or category in a system of biological classification.
  taxonomy
  The study of the principles and practice of classification.
  tegmen
  The inner layer of the testa (seed coat). It develops from the inner integument of the ovule.
  tendril
  Any slender organ modified from a stem, leaf, leaflet, or stipule and used by climbing plants to cling to an object.
  tepal
  A segment of a perianth, either sepal or petal; usually used when all perianth segments are indistinguishable in appearance.
  terete
   
  Circular in cross-section; more or less cylindrical without grooves or ridges.
  terminal
  Situated at the tip or apex.
  ternate
  In groups of three; of leaves, arranged in whorls of three; of a single leaf, having the leaflets arranged in groups of three.
  terrestrial
  Of or on the ground; of a habitat, on land as opposed to in water (aquatic), on rocks (lithophytic), or on other plants (epiphytic).
  testa
  The seed coat.
  tetrad
  A group of four; usually used to refer to four pollen grains which remain fused together through maturity (e.g. in the Epacridaceae).
  tetragonal
  Square; having four corners; four-angled, e.g. the cross-sections of stems of herbaceous Lamiaceae.
  tetramerous
  In four parts, particularly with respect to flowers; four parts in each whorl. See also trimerous and pentamerous.
  tetraploid
  Having four complete sets of chromosomes in each sporophyte cell.
  tetraspore
  The asexual spore of red algae. It is so named because each sporangium produces just four spores. See Rhodophyceae.
  thalamus
   1.  A synonym for receptacle.
  2.  The inflorescence disk of members of the Asteraceae.
  3.  A calyx, as used by Carl Linnaeus.
  thallus
  The "vegetative" part (part other than sexual fruitbodies) of a lichen  that has both the fungus (mycobiont) and photobiont; plural thalli
  theca
  One of the usually two synangia in which pollen is produced in flowering plants. It consists of two fused sporangia known as pollen sacs. The wall between the pollen sacs disintegrates before dehiscence, which is usually by a common slit.
  thorn
  A sharp, stiff point, usually a modified stem, that cannot be detached without tearing the subtending tissue; a spine. Compare prickle.
  throat
  The opening of a corolla or perianth.
  thyrse
  A branched inflorescence in which the main axis is indeterminate (racemose) and the lateral branches determinate (cymose).
  tomentum
  A dense covering of short, matted hairs. Tomentose is often used as a general term for bearing an indumentum, but this is not a recommended use.
  toothed
  Having a more or less regularly incised margin.
  torus
  See receptacle.
  transmitting tissue
  See pollen transmitting tissue.
  trapeziform
  1.  Like a trapezium (a four-sided figure with two parallel sides of unequal length).
  2.  Like a trapezoid (a four-sided figure, or quadrilateral, with neither pair of sides equal); sometimes used erroneously as a synonym for rhombic.
  tree
  A woody plant, usually with a single distinct trunk and generally more than 2–3 metres (6.6–9.8 ft) tall.
  triad
  A group of three.
  triangular
  Planar and with 3 sides.
  tribe
  A taxonomic grouping that ranks between genus and family.
  trichome
  In non-filamentous plants, any hair-like outgrowth from the epidermis, e.g. a hair or bristle; sometimes restricted to unbranched epidermal outgrowths.
  trifid
  Split into three parts. See also bifid.
  trifoliate
  A compound leaf of three leaflets; for example, a clover leaf.
  trifoliolate
  See trifoliate.
  trigonous
  Triangular in cross-section and obtusely angled. Compare triquetrous.
  trimerous
  In three parts, particularly with respect to flowers; having three parts in each whorl. See also tetramerous and pentamerous.
  trinerved
  Having three nerves or veins.
  triplinerved
  (of leaves) Having three main nerves with the lateral nerves arising from the midnerve above the base of the leaf.
  triquetrous
  More or less triangular in cross-section, but acutely angled (with 3 distinct longitudinal ridges). Compare trigonous
caption: Tendrils of Cucurbita pepo, some supporting the stem on the frame, some failing to find a point of attachment.
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