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Term Glossary
Term Definition
abaxial side away from stem or axis; back, dorsal, or lower surface of leaf or costa (opposed to adaxial)
abortive defective or terminated development; e.g., imperfectly developed spores
abrupt changing suddenly rather than gradually, as in leaves quickly constricted to a narrow acumen
acaulescent stemless; referring to plant with extremely short internodes
accessory chromosome a supernumerary, or B-, chromosome. Its uncritical use in bryophyte cytology as a synonym for m-chromosome has led to inaccuracy
accrescent increasing in size
acicular needle-shaped
acidophile growing in acid habitats (opposed to basiphile)
acidophilous acid-loving
acinaciform sickle-shaped
acrandrous with antheridia produced at apex of stem
acrocarpous with gametophyte producing sporophyte at apex of a stem or main branch. Acrocarpous mosses generally grow erect in tufts (rather than mats) and are sparsely or not branched (opposed to pleurocarpous)
acrodendrophilous thriving in tree tops
acrogynous having archegonia produced at the apex of a stem or branch, accompanied by loss of apical cell and termination of further shoot growth (opposed to anacrogynous)
acropetal an ascending series; tissues or organs developing or maturing from the base toward the apex, youngest arise at the apex (opposed to basipetal)
acrophilous thriving in alpine regions
acroscopic toward the apex; applied to the triangular surface of a merophyte in direct contact with the apical cell (opposed to basiscopic)
actinomorphic radially symmetric
acumen a slender, tapering point
acuminate slenderly tapered with an angle of less than 45 |1; longer than acute
acute sharp pointed, with terminal angle less than 90 |1 but greater than 45 |1
adaxial side toward stem or axis; ventral or upper surface of a leaf or costa (opposed to abaxial)
adherent having two dissimilar parts or organs in contact with one another but not fused; e.g., bracts and perianth of leafy liverworts (cf. coherent, adnate)
adnate fused together; the fusion of unlike parts, i.e. perianth and bract (cf. connate, adherent)
adventitious plant organs produced in atypical place,i.e., rhizoids arising from leaf or costal cells
adventive introduced; e.g., adventive species or, in reference to a structure that arises from a dedifferentiated cell, such as an adventive branch (Cephalozia)
aerophyte a plant growing on aerial parts of another plant (see epiphyte)
aeruginose bluish green in color
aggregate collected together, clustered
air chamber specialized internal air-containing cavity common in most complex thalloid liverworts; e.g., Marchantiales
air pore minute opening in the upper epidermis of most complex thalloid liverworts, functioning in gas exchange and water regulation; bordered by one or more rings of modified epidermal cells (syn. pneumathodes); breathing pore -- a specialized compound air pore that contains 3-5 enlarged, hygroscopically active cells at the base of the barrel structure, allowing for closure; e.g., Pressia; compound pore -- air pore bordered by both superficial cells arranged in concentric rings and an internal, cylindrical or barrel-shaped structure of epidermal origin; e.g., Marchantia; simple pore -- air pore bordered only by superficial cells (cf. stoma)
alar cells referring to cells at basal margins (angles) of a leaf; these cells are often differentiated in size, shape or color from other leaf cells, e.g., Dicranum; see auricle
allopatric taxa inhabiting separate areas of distribution
alluvium mineral rich soil deposited by water (alluvial soil); e.g., soils of flood plain
alpestrine pertaining to high mountains; regions above timberline
alpine the arctic zone of a mountain; above timberline
alveolate with depressions on the surface, sometimes applied to spores, e.g., species of Fossombronia; (cf. foveolate, areola)
amentulum the so-called catkins of the male androecium in Sphagnum
amorphous shapeless, without regular or definite form
amphigastrium underleaves in leafy liverworts; in a few mosses, smaller leaves on the upper (Racopilum) or lower (Helicophyllum) stem surface, variously differentiated from the lateral leaves; see underleaf
amphithecium in bryophytes the outer part of the embryonic capsule that gives rise to all tissues from the epidermis to the outer spore sac; also producing the spore sac in Sphagnum and hornworts (see endothecium)
amplectant embracing; clasping by the base
amplexicaulous clasping the stem, as the base of a leaf
anacrogynous having archegonial production in a lateral position on a stem, branch or thallus, from superficial initials and without loss of apical cell function (opposed to acrogynous)
analogous structures or organs with similar functions that do not have a common phylogenetic origin; e.g., stomata and air-pores (opposed to homologous)
anastomose union of one structure with another; interconnecting; sometimes applied to irregularly divided peristome teeth
ancophilous thriving in steep valleys or canyons
androcyte cell that matures into a spermatozoid (antherozoid)
androcyte mother cell cell that divides to form two androcytes
androecial branch specialized branch bearing antheridia
androecium antheridia and surrounding bracts (perigonium or involucre); the "male inflorescence."
androgametophyte male gametophyte (see gynogametophyte, androgynogametophyte)
androgenous bearing androecia
androgonial cell internal initial of a developing antheridium that gives rise to androcyte mother cells
androgynogametophyte autoicous or synoicous gametophyte (see androgametophyte, gynogametophyte)
androgynous see monoicous
angular cells see alar cells
anisophyllous having stem and branch leaves morphologically dissimilar; e.g., Sphagnum, Mittenothamnium, Thuidium; or bearing two distinct types of leaves; e.g., Hypopterygium, Racopilum, most leafy liverworts (opposed to isophyllous)
anisosporous having spores with a bimodal (or multimodal) distribution of size, generally the smaller spores giving rise to male gametophytes; often associated with nanandry. True heterospory (separate micro- and megasporangia) does not occur in bryo-phytes
annotinous displaying yearly growth, frequently evident by periodic clusters of leaves along a stem; e.g., Polytrichum, Hylocomium splendens
annual of one year's duration; completing life cycle in one year (see ephemeral)
annular ringlike; leaves or branches arranged in a circle; e.g., Rhodobryum, Philonotis
annular thickenings ring-like thickenings extending over both tangential and radial cell walls; e.g., liverwort capsules
annulus in stegocarpous mosses a zone of variously differentiated cells between the capsule urn and operculum, facilitating opening of the capsule; cf. valve
anodic the ascending direction of apical cell segmentation; applied to the rectangular merophyte surface that is oriented towards the segmentation spiral (opposed to kathodic)
anterior in transversely inserted leaves, the side or surface oriented away from the axis; dorsal or abaxial (opposed to posterior)
antheridiophore specialized antheridium-bearing branch; e.g. Marchantia; the male gametangiophore
antheridium male gametangium; a multicellular globose to broadly cylindric, stalked structure containing spermatozoids (syn. androgonium)
antherozoid see spermatozoid
anthracine coal-black
anthropochorous plants that are distributed by the action of man
antical the dorsal surface of a stem; the leaf margin oriented towards the shoot apex of a longitudinal or obliquely inserted leaf (opposed to postical)
anticlinal perpendicular to the surface; radial; at right angles to the free or exposed surface; applied to cell divisions that are perpendicular to the free surface (opposed to periclinal; see transverse)
antrorse directed upward or forward (opposed to retrorse)
aperturate a spore with one or more pores in the exine
aperture an opening or hole
apical at apex, summit or point of a structure
apical cell a single meristematic cell at the apex of a shoot, thallus, leaf or other organ that divides repeatedly to form new cells
apical lamina in Fissidens the part of the leaf above or distal to the vaginant and dorsal laminae
apical notch marginal indentation in which the apical cell is located in thalloid hepatics; provides an emarginate appearance to the thallus apex; e.g., Metzgeria
apiculate abruptly short-pointed (mucronate is shorter; cuspidate is longer and stouter)
apiculus a short, abrupt point
apogamy development of sporophyte directly from gametophyte, without fusion of gametes; such sporophytes have the same chromosome number as the gametophyte from which they have been derived (cf. apospory, dipiospory)
apolar spore spore with no distinct polarity, e.g. spores lacking a conspicuous triradiate ridge or pore (opposed to polar spore)
apomixis reproduction by means other than fertilization, i.e., development of sporophyte directly from an egg without union of gametes; cf. apogamy; production of sporophyte from fusion of ovum (egg) with ventral canal cell (reported in Sphagnum); also used for any form of vegetative reproduction, e.g. production of gemmae
apophysis a strongly differentiated, sterile neck at the base of a capsule, between seta and urn; e.g., Trematodon, Polytrichum, Splachnum (see hypophysis, neck)
apospory development of gametophyte from sporophyte tissue without intervening meiosis; such gametophytes have the same chromosome number as the sporophyte from which they have been derived (cf. apogamy, diplospory)
appendicula short transverse projections formed from horizontal wall-pairs, often borne on endostomial cilia (see trabecula); sometimes used in liverworts for the presence of cilia, auricles or other appendages at leaf bases
appendiculate with short, thin, transverse projections (see appendicula, nodulose)
appressed closely applied, as leaves lying close or flat against the stem
approximate drawn together but not touching as leaves that come near each other but do not overlap (also: +, more or less)
arboreal growing on trees (cf. corticolous)
archegoniophore a specialized archegonial-bearing branch; the female gametangiophore, e.g.; Marchantia
archegonium female gametangium or sex organ; a multicellular, flask-shaped structure consisting of a stalk, venter, neck and containing an ovum (see gametangium; syn. gynogonium)
archesporium mass of cells within the capsule, ultimately giving rise to spores and sometimes elaters (see sporocyte)
arcuate curved
arenicolous growing on sand or sandy places
areola small angular or polygonal surface areas differing in color or structure from the surrounding area, forming a pattern or network; e.g., spores of many Riccia species
areolation the cellular network of a leaf or thallus
argillicolous dwelling on clay
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