Botany Terms Starting With O
Botany Glossary: O
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Ornithophilous
/ or-nih-THOF-il-us / · Greek ornithos (bird) + philos (loving)
Ornithophilous describes flowers that are pollinated by birds, typically through structural and chemical traits that attract species such as hummingbirds, sunbirds, or honeycreepers.
Ornithophilous flowers display a suite of traits shaped by bird sensory capabilities and foraging behavior: long tubular shapes that accommodate curved beaks, bright red or orange coloration in the 600-nanometer wavelength range that birds perceive vividly, and copious nectar with 15 to 30 percent sugar concentration to fuel high metabolic demands. Pollen is positioned to contact the bird’s head or upper beak during feeding, ensuring transfer between flowers. These flowers typically lack fragrance because most birds have weak olfactory ability compared to insects.
Trumpet creeper (Campsis radicans), sage, and fuchsia exemplify the ornithophilous syndrome, producing nectar at delivery rates of 1 to 5 milligrams per flower per hour.
The sword-billed hummingbird (Ensifera ensifera) of the Andes has a bill longer than its entire body, reaching up to 10.5 centimeters, and pollinates passionflowers (Passiflora mixta) whose corolla tubes match that length so precisely that no other pollinator can reach the nectar.
Ornithophilous flowers must be strongly scented to attract their pollinators. Bird-pollinated flowers are typically odorless or nearly so, relying on vivid color and abundant nectar rather than scent to draw visitors.
In trumpet creeper (Campsis radicans), orange-red tubular flowers are visited repeatedly by ruby-throated hummingbirds (Archilochus colubris), which brush pollen onto their foreheads while probing for nectar. A single hummingbird may visit more than 1,000 flowers per day during peak foraging, making it a highly effective pollinator of ornithophilous plants across its range.
Ornithophily
/ or-nih-THOF-il-ee / · Greek ornithos (bird) + philos (loving)
Ornithophily is pollination carried out by birds, in which species such as hummingbirds, sunbirds, and honeycreepers transfer pollen between flowers while feeding on nectar.
Ornithophilous plants typically produce large, sturdy flowers with abundant dilute nectar to fuel the high metabolic demands of hovering or perching birds, and most lack floral scent because birds have poor olfactory ability compared to insects. Flowers adapted for bird pollination commonly display red or orange coloration, wavelengths that birds detect sharply but that are less visible to many competing insect visitors. Hummingbirds in the Americas pollinate more than 7,000 plant species, visiting flowers whose tubular shapes match the length and curvature of specific hummingbird bills.
This tight morphological matching between flower tube length and bill length, documented in Andean passionflowers and the sword-billed hummingbird (Ensifera ensifera), reduces nectar theft by insects and increases pollen transfer efficiency.
The Cape sugarbird (Promerops cafer) of South Africa pollinates king protea (Protea cynaroides) by pressing its face into the large flower head to reach nectar, picking up pollen on its forehead feathers. King protea flowers can measure up to 30 centimeters across, making them among the largest bird-pollinated flower heads in the world.
Ornithophily and anemophily both describe the same general process of pollen transfer. Ornithophily specifically means pollination carried out by birds, while anemophily means pollination by wind; the two syndromes involve entirely different flower structures and pollen properties.
In the cloud forests of Costa Rica, the purple-throated mountain-gem hummingbird (Lampornis calolaemus) pollinates Heliconia tortuosa by hovering at curved orange bracts and inserting its bill to reach nectar pools up to 4 centimeters deep. Pollen deposited on the bird's bill and crown is carried to the next flower, completing ornithophily across forest patches separated by hundreds of meters.
Osmotic Potential
/ oz-MOT-ik poh-TEN-shul / · Greek osmos (push) + Latin potentia (power)
Osmotic potential is the component of water potential that reflects the effect of dissolved solutes on water movement, becoming more negative as solute concentration increases and driving water toward regions of higher solute concentration.
In plant cells, solutes such as sugars, inorganic ions, and organic acids dissolved in the vacuole and cytoplasm lower osmotic potential below zero, typically ranging from about -0.5 megapascals in well-watered mesophyll cells to below -3 megapascals in drought-stressed tissues. Water moves by osmosis from regions of less negative osmotic potential, such as the soil solution, into regions of more negative osmotic potential, such as root hair cells, without requiring metabolic energy. This gradient drives water uptake across root membranes and maintains turgor pressure, which keeps non-woody plant tissues firm.
Guard cells regulate stomatal opening partly by actively accumulating potassium ions, which lowers their osmotic potential and draws water in, increasing turgor and bowing the cells apart to open the pore.
Desert succulents such as the quiver tree (Aloidendron dichotomum) maintain osmotic potentials as low as -4 megapascals in their leaf cells during dry seasons, a value low enough to extract water from soils that would be too dry for most crop plants to survive.
Differences Between Plant and Animal Cells →Osmotic potential and water pressure are the same measurement. Osmotic potential specifically describes the contribution of dissolved solutes to water movement, while turgor pressure, or pressure potential, is the separate physical force exerted by the cell wall against an expanding cell.
In root hair cells of sunflower (Helianthus annuus), dissolved minerals and sugars lower osmotic potential to roughly -0.6 megapascals, while the surrounding soil solution sits near -0.03 megapascals. Water moves down this gradient into the root hair by osmosis, generating the turgor pressure that drives cell expansion during root elongation.
Ovule
/ OV-yool / · Latin ovulum (little egg)
Ovule is a structure within the ovary of a seed plant that contains the female gametophyte and, after fertilization, matures into a seed.
An ovule consists of the nucellus, the central nutritive tissue surrounding the embryo sac; one or two protective integuments that will harden into the seed coat; and the funiculus, the stalk attaching the ovule to the placenta of the ovary wall. After double fertilization in angiosperms, the egg cell becomes the embryo and the central cell develops into the endosperm, while the integuments mature into the testa. Ovule number per ovary ranges from one in cherries (Prunus avium) to hundreds of thousands in orchids, where each dust-like seed weighs less than 2 micrograms and carries almost no nutrient reserves.
Ovule position and orientation within the ovary, described by terms such as anatropous, orthotropous, and campylotropous, differ systematically among plant families and have been used since the 19th century as taxonomic characters to distinguish related groups. Anatropous ovules, in which the body is bent 180 degrees so the micropyle faces the funiculus, are the most common form among flowering plants.
An ovule is already a seed. An ovule becomes a seed only after fertilization and the subsequent maturation of the embryo and seed coat; an unfertilized ovule contains only the female gametophyte and will abort if pollination does not occur.
In garden peas (Pisum sativum), each ovary typically contains 6 to 10 ovules arranged along the ventral suture of the carpel. After fertilization, each ovule develops into a pea seed, with the funiculus leaving a visible scar called the hilum on the mature seed coat.