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Term	Definition
Predation	Referring to an interaction between two organisms one that lives on and at the expense of another, e.g., an insect larva that eats the embryo of a hickory nut or a species of Loranthaceae taking nutrients from a host plant.
Prickle	A sharp, pointed outgrowth of the epidermis of stems, leaves and other plant parts; e.g., on the trunk and branches of Ceiba pentandra (Bombacaceae) and Jacaratia spinosa (Caricaceae), on the stems of Smilax spp. (Smilacaceae), and on the stems and leaves of many species of Solanum.
Primary hemiepiphyte	Referring to a plant (e.g., Clusia spp. and species of Araceae) that begins its epiphytic life without a connection to the ground but later develops aerial roots that reach the ground.
Primary leaflet	The first division of a compound leaf.
Primary rachis	The main rachis of a compound leaf or a compound inflorescence.
Primary vein	The thickest vein of a leaf (Hickey, 1973)
Primary venation	The largest (in diameter) vein (e.g., in camptodromous venaton) or veins (e.g., in actindodromous venaton) in a leaf blade. Same as midrib.
Prominent (diminuitive = prominulous)	Raised above the surface; e.g., the veins of a leaf or a seed.
Prop roots	Aerial, densely packed, adventitious roots that are circular in transverse section. Prop roots do not allow light to be seen through them whereas stilt roots do.
Prophyll	In monocots, the first leaf produced on a branch and located between the branch and the main axis; often two-keeled.
Prostoma (plural = prostomata)	An indented and/or membranous area through which plant-associated ants bore into the hollow chambers of the trunks and stems; e.g., in many species of Cecropia (Cecropiaceae).
Prostrate	Creeping flat along the ground, usually referring to stems growing along the ground that produce roots at their nodes. Same as repent.
Protandry (protandrous)	Referring to a flower in which the pollen is shed before the stigma is receptive. Sometimes called proterandry (proterandrous).
Prothallus (plural = prothalli)	The structure representing that part of a fern's life cycle between the germination of the haploid spore and the formation of the zygote. Fern prothalli are small, green, often heart-shaped, and bear the archegonia and antheridia where the egg and sperm are produced, respectively.This is the gametophyte generation of ferns and is completely independent of the sporophyte generation. Only those who know what they are looking for can find prothalli because they are small and hidden among the debris on the ground.
Protogyny (protogynous)	Referring to a flower in which the stigma is receptive before the pollen is shed. Sometimes called proterogyny (proterogynous).
Protologue	A scientic publication in which a new species is described or a scientific publication in which more than one new species are described, in the latter case each of the descriptions is the protologue of the new species.
Proximal	Near to the place of attachment. Opposite of distal. Same as basal.
Proximal	The part of an organ closest its the point of attachment.
Pseudanthium (plural = pseudanthia)	A false flower; e.g., the inflorescence of species of Asteraceae and Dalechampia (Euphorbiaceae).
Pseudaril	In Burseraceae, soft aril-like tissue that covers part or all of the pyrene and attracts dispersal agents.
Pseudobulb	In Orchidaceae, a specially modified stem that is variously swollen and stores food and water. Pseudobulbs are common in epiphytic but are lacking in terrestrial species.
Pseudocarp	Several small "fruits" surrounded by accompanying parts, such as that of Siparuna (Siparunaceae), in which the separate carpels are surrounded by a fleshy hypanthium, or the syconia of figs in which the the achenes are surrounded by hollow stem ends.
Pseudostem	The apparent stem of Musa (Musaceae), Phenakospermum (Strelitziaceae), and some other monocots which is actually a cylinder formed by overlapping leaf bases.
Pseudostipule	A leaf (e.g., in some species of Aristolochiaceae) or leaflet (e.g., in some species of Trichilia, Meliaceae) that resembles a stipule; in some Bignoniaceae, a bud scale derived from the axillary buds that resembles a stipule.
Pseudosyncarpous	In the Annonaceae, referring to fruits in which the carpels seem to be connate, but in reality are free or almost free (e.g., species of Duguetia in the Annonaceae).
Pubescence (adjective = pubescent)	Referring to plants with some or all of their parts covered with trichomes.
Pulvinate	Possessing pulvini.
Pulvinulus (pl. = pulvinulus, adj. = pulvinate or pulvinulate)	An enlargement at the base of the petiole or petiolule of leaves.
Pulvinus (plural = pulvini)	An enlargement of a portion of the petiole, without an apparent function (e.g., Protium, Burseraceae) or sometimes controlling the orientation of the leaf or leaflet (e.g., Mimosa polydactyla and M. pudica, Fabaceae).
Punctate	With small dots or streaks that transmit light when held against a light source, with sunken glands, or colored dots; especially easy to see in species of Myrtaceae and Rutaceae.
Punctation (adj. = punctate)	A translucent glandular dot or streak such as found on the leaves of Myrtaceae or Rutaceae or an opaque dot found in other families, such as the Lecythidaceae.
Pustule (adj. pustulate)	A small pimple-like eruption from the surface of part of a plant; e.g., from the hypanthium.
Pustule (adj. pustulate)	A small pimple-like eruption from the surface of part of a plant; e.g., from the hypanthium.
Pyrene	In the Burseraceae, the part of the fruit surrounding a seed or seeds that is derived from the endocarp and is sometimes surrounded by a pseudaril. Similar to a stone but we restrict stones to only drupes or drupelets with a single seed.
Pyxidium, pyxidiate	A capsular fruit with circumscissile dehiscence.
Quaternary vein	Referring to fourth order leaf veins which are intermediate in diameter between tertiary and quinary veins.
Raceme	An indeterminate inflorescence with a single axis, the flowers borne on pedicels of more or less equal length, and the uppermost flower the youngest. Compare with spike.
Rachilla	The axis of a spikelet of a Cyperaceae or a Poaceae along which are placed the florets.
Rachis (alt. spelling = rhachis)	The axis of a compound leaf (excluding the petiole) or of an inflorescence (excluding the peduncle); in legumes, that part of the leaf axis bearing leaflets of any order.
Rachlla	A secondary axis of an inflorescence; e.g., the axis of the spikelet in Poaceae or the axis that bears the flowers in Arecaceae.
Radial thickenings	A series of protuberances arranged in a spoke-like pattern around the top of the supracalycine zone just outside the line of opercular dehiscence.
Radially symmetrical flower	A flower, capable of being divided, by more than one line passing through the middle of the flower, into two equal parts that are mirror images of one another; e.g., in Gustavia (Lecythidaceae), species of Myrtaceae, and species of Rubiaceae. Same as actinomorphic, polysymmetric, and regular flowers and opposite of zygomorphic, monosymmetric, bilateral, and irregular flowers. This term can refer to other plant parts as well.
Radiate capitulum (head)	Inflorescence of Asteraceae with marginal ray flowers and central disk flowers.
Radicle	The lower portion of the embryo that develops into the root. Same as hypocotyl.
Rain forest	A low, large tree dominated forest found from sea level to around 500 meters in Latin America. Dominant trees families are members of the Burseraceae, Chrysobalanceae, Lecythidaceae, Moraceae, Sapotaceae etc. but the composition of the forest can vary geographically, for example, the rain forests of eastern Brazil are sometimes dominated by species of Myrtaceae. The largest trees in neotropical rain forests usually do not exceed 65 meters in height. True rain forest does not have a marked tree season but currently the rain forest concept does include some forests with short dry seasons.
Ramet	An individual part of a clone, e.g., an offshoot.
Ramiflorous	Producing flowers on leafless branches or leafless parts of stems; a special type of cauliflory. Compare with cauliflorous.
Ramiflorous inflorescence	Refers to inflorescences that arise from the branches. Inflorescences that arise from the trunk are called cauliflorous. The branches can be much smaller in diameter than those shown here.
Ramiflorous inflorescence	Refers to inflorescences that arise from the branches. Inflorescences that arise from the trunk are called cauliflorous. The branches can be much smaller in diameter than those shown here.
Raphe	A ridge on a seed formed by the fusion of the funicle to the seed coat, usually indicated by a scar after the seed has been formed.

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