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Term	Definition
Horn	An flora appendage shaped like an animal’s horn; e.g., the horn of the corona of Apocynaceae subfamily Asclepiadoideae.
Hypanthium	A floral tube made up of fused parts of the perianth and sometimes including receptacular tissue. The tube may be free from the ovary as in perigynous flowers or it may be fused to the ovary as in epignynous flowers.
Hypochile	The basal portion of a complex lip in Orchidaceae.
Hypogynium	A disc or cuplike structure below the ovary of some Cyperaceae.
Hypogynous ovary	Referring to a flower in which 1) the sepals, petals, and stamens are free from one another and arise from beneath the ovary, e.g., the flowers of Ranunculaceae or 2) bristles or other structures as well as stamens arise from below the ovary, e.g., the bristles of some species of Cyperaceae and the modified bracts of species of Poaceae. Compare with epigynous and perigynous.
Hypopeltate anther	Referring to an anther with the filament attached above the base and with the part of the anther that is prolonged downward facing away from the center of the flower.
Imbricate-contorted aestivation	A type of aestivation in which one edge of the structure (e.g., a petal) is above and the other below the structure on each side of it.
Imperfect flower	Referring to a flower that possesses only male (= staminate flower) or female (= pistillate flower) flowers .
Incomplete flower	A flower with at least one of the whorls of floral parts missing; i.e., calyx, corolla, stamen(s), or gynoecium. Compare with complete flower.
Inferior ovary	An ovary in which the floral parts (calyx, corolla, and stamens) arise from the summit; e.g., in Rubiaceae and Asteraceae.
Integument	The outer covering of the ovule that develops into the testa or seed coat; it may be composed of one or two layers, the inner and outer integuments, respectively.
Intine	The inner layer of the two-layered wall of a pollen grain. Compare with exine.
Intrastaminal	Placed inside of the stamens; e.g., the discs of most Anacardiaceae and Meliaceae.
Intrastaminal disc	A fleshy, lobed, or annular nectariferous structure found within flowers between the stamens and the pistil. Preferred spelling is disc. Not to be confused with disk flower.
Intruded placenta	A parietal placenta that penetrates into the locule such that the placentation appears to be axile; e.g., in some species of Flacourtiaceae.
Involucrum	An adherent group of hairs arising from the style head in the Apocynaceae and often forming a ring that closes off the corolla. Sometimes called the ring.
Irregular flower	A flower capable of being divided into only two equal parts (mirror images) by a line passing through the middle of a flower, i.e., other lines passing the middle of the flower will not give mirror images of one another; same as zygomorphic, monosymmetric, and bilaterally symmetrical, flowers and opposite of actinomorphic, monosymmetric, radially symmetrical, and regular flowers. This term can refer to other plant parts as well.
Keel	Ridged like the bottom of a boat; same as carinate.The two lower, united petals of the flower of most species of Fabaceae subfamily Papilionoideae.
Labellum	Same as lip.
Laminar placentation	A type of parietal placentation in which the ovules arise along the surface (rather than the margins) of the carpels. Compare with marginal placentation; see placentation.
Lateral style	Referring to a gynobasic style that arises from the base and side of the ovary.
Lemma	The lower of the two bracts that enclose the floret of the Poaceae, located above the glumes. Compare with palea.
Ligulate flower	A zygomorphic flower with a straplike corolla found in the Asteraceae tribe Lactuceae. Differring from a ray flower by having five instead of three lobes.
Ligule coiled	Referring to a ligule of Lecythidaceae that coils inward one or more times. In species with coiled ligules, the coiled part with the vestigial stamens is called the androecial hood. Species of Eschweilera and Couratari are the only species that have coiled ligules and they are the only species that have nectaries hypothesized to be derived from vestigial stamens.
Ligule not coiled	Referring to a ligule of Lecythidaceae that does not make a full coil inward. On the Osa Peninsula only Lecythis mesophylla is known to have this type of ligule. It does, however, have vestigial stamens that are swept inward but they do not form a complete coils as found in species of Eschweilera and Couratari. In L. mesophylla, the hood is the part of the ligule that possesses vestigial stamens.
Lip	The median petal of Orchidaceae which is usually highly modified and different from the two lateral petals, the lip of orchids often plays a crucial role in the plant's pollination; one of the two divisions of a bilabiate corolla, e.g., in the Lamiaceae.
Lodicule	A small, colorless scale appressed to the ovary of most Poaceae that may represent a vestige of the perianth.
Longitudinal anther dehiscence	Same as lateral anther dehiscence.
Lophate	Referring to a type of pollen ornamentation in which the exine is raised in a network of ridges surrounding depressions.
Male flower	Referring to unisexual flowers with functional stamens but without functional gynoecia (pistillodes may be present). Same as pistillate flower.
Marginal placentation	A type of parietal placentation in which the ovules arise along the margins of the carpel. Compare with laminar placentation; see placentation.
Megagametophyte	The female gametophyte of angiosperms (flowering plants). Same as embryo sac.
Mentum	In some Orchidaceae, a lateral (sometimes nectariferous) projection from the base of the column formed by the fusion of the base of the column and the lateral sepals; common in Scaphyglottis.
Mesochile	The central portion of a complex lip in Orchidaceae.
Microgametophyte	See pollen.
Micropyle	An opening in the integuments of the ovule through which the pollen tubes generally penetrate.
Monad	A pollen grain that occurs singly. Compare with tetrad.
Monadelphous	Referring to stamens united by their filaments into a single group.
Monochlamydeous	Referring to a flower with a single whorl of perianth parts; same as a uniseriate perianth. Compare with heterochlamydeous.
Monocolpate	A pollen grain with a single colpus.
Monosulcate pollen	Referring to a pollen grain with one groove or furrow.
Monosymmetric flower	A flower capable of being divided into only two equal parts (mirror images) by a line passing through the middle of a flower, i.e., other lines passing the middle of the flower will not give mirror images of one another; same as zygomorphic, bilaterally symmetrical, and irregular flowers and opposite of actinomorphic, monosymmetric, radially symmetrical, and regular flowers. This term can refer to other plant parts as well.
Monothecous	Referring to an anther with a single theca.
Nectar	A sugar solution of varied composition produced by nectaries within flowers to attract pollinators or by extrafloral nectaries to attract insects that protect the plant from predation.
Nectar guide	Markings on a flower that apparently serve to guide pollinators to the nectar. Some are visible to humans, but others are apparent to humans only through ultraviolet photography. Same as honey guide, a term not recommended because bees, not plants, produce honey.
Nectar ring	In some Passifloraceae, a low narrow ring situated below the operculum.
Nectar spur	A tubular-like projection from the sepals or petals that produce and retain nectar as a reward for pollinators; in many orchids nectar spurs are hollow, tubular projections formed at the base of the lip which contain nectar rewards for pollinators.
Nectariferous disc	A more or less fleshy and elevated part of the receptacle, situated between the perianth and the stamens or between the stamens and the gynoecium, which functions in the production of nectar. Also referred to simply as a disc.
Nectary	A tissue or structure of flowers that produces nectar.
Nectary scale	A appendage (bracteole-like) located between the flowers of some Capparidaceae upon which the nectary gland (= nectary) is located.

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