Plant Science Terms - S

Sagittate - arrowhead-shaped, with two pointed lower lobes projected downward

Samara - indehiscent dry fruit with either one or two seeds, in which pericarp bears a flattened wing-like outgrowth. The “helicopter seeds" of the maple trees are double-samaras

Sand - coarsest type of soil particle

Sandy Soil - Sandy soil is composed of many irregular to rounded tiny grains of sand, as opposed to the many tiny plate-like soil particles that make up a clay soil. Sandy soil drains very quickly and doesn't hold on to fertilizer well

Sanitation - removal and disposal of infected plant parts; decontamination of tools, equipment, hands, etc

Saprophyte - organism that can subsist on non-living matter

Sapwood - newly formed lighter outer wood located just inside the vascular cambium of a tree trunk and active in the conduction of water

Saturation - This is when the entire root zone of a plant is moist after watering

Scab - slightly raised, rough areas on fruits, tubers, leaves, or stems

Scabrous - leaf textures that are rough to the touch; texture of sandpaper

Scaffold branches - principal branches of a tree or shrub arising from the trunk or another main branch to form the plant’s framework

Scaffold whorl - first three to four branches on a trunk uniformly spaced

Scale - modified leaf that protects a bud; type of insect pest

Scaling - type of propagation that separates bulb scales from the mother bulb to induce the formation of bulblets

Scalping - excessive removal of turf leaves by close mowing, resulting in a brown, stubbly appearance

Scarification - chemical or physical treatment given to some seeds to break, weaken, or soften the seed coat sufficiently for germination to occur. Methods include; scratching or rupturing the seed coat with sandpaper, nicking it with a knife, or degrading it with concentrated acid

Scion - upper part of the union of a plant graft or cultivar that is grafted onto a separate rootstock, consisting of a piece of shoot with dormant buds that will produce the stem and branches

Sclerites - insects’ bodies are separated into segments, and the cuticle of each segment is formed into several hardened plates called sclerites

Sclerotia - seed-like, compact masses of fungal tissue that allow fungi to survive unfavorable conditions

Sclerotium - hardened brown or black fungal survival structure. May be round or irregular

Scorch - when plants receive too much sun, pesticide, or fertilizer the foliage may look brown or yellowish from the necrosis and desiccation of leaf tissue, starting at the margins .  The foliage in these cases is said to be scorched

Scout - assessing pest pressure and plant performance. The first step in any IPM plan

Secondary growth - growth that increases the girth of stems or roots without elongating them. Secondary growth is seen in some dicots but not in monocots

Secondary nutrient - nutrient needed by plants in a moderate amount: calcium, magnesium, and sulfur. (See also Macronutrient, Primary nutrient)

Secondary root - type of root system that forms after the primary root emerges from a seed and branches outward

Seed - reproductive structure formed from maturation of an ovule that contains an embryo and stored food and encased in a protective seed coat that occurs as, or in, mature fruits


Seed, certified - seed lot inspected to meet minimum standards and to ensure trueness to type for a given cultivar

Seed coat - protective outer layer of a seed that provides protection for the enclosed embryo

Seed coat impermeability - caused by a hard seed coat that is impermeable to water, preventing the seed from germinating

Seed dormancy - adaptive feature of some plants to keep the seeds from germinating until conditions exist that favor seedling survival

Seed leaf - see Cotyledon 

Seed scarification - involves breaking, scratching, or softening the seed coat so that water can enter and begin the germination process

Selective pesticide - pesticide that kills only certain kinds of plants or animals; for example, 2,4-D kills broadleaf lawn weeds but leaves grass largely unharmed

Self-cleaning - term used when a plant sheds old blooms without human help.  This is not the same as dead-heading which involves removing seed heads to prevent seed set

Self-fertile - plant that produces seed with its own pollen

Self-fruitful - plant that bears fruit through self-pollination

Self-pollination - process by which pollen is transferred from the pollen producing section of the plant (anther) to the pollen receiving part of the plant of the same flower (stigma), or in different flowers on different plants of the same species, variety, or cultivar

Self-sterile - plant that needs pollen from another species, variety, or cultivar (e.g., cross-pollination)

Self-unfruitful - plant that requires another variety for pollination. (See Pollinizer)

Semihardwood cuttings - cuttings made from woody, broad-leaved evergreen species such as ligustrum and holly

Semitrailing - caneberries that are fully trailing the first year but become more erect the following year

Senescence - aging process; breakdown of cellular structures leading to death; used to describe a plant that is in the process of going dormant for the season, although technically only the parts that are dying (the leaves) are becoming senescent

Sepals - outer covering of the flower when it is in the bud stage and form the outermost whorl of the flower. They are leaf-like in structure and usually green, but can be colored and look like petals, as in tulips. They may fold back as in roses or remain upright as with carnations. Together, all the sepals form the calyx

Separation - form of asexual reproduction or propagation by which plants that produce bulbs or corms multiply by utilizing the naturally detachable parts

Serrate - having small, sharp teeth pointing toward the apex

Serrate leaf - leaf with serrations or "teeth" along the edge of the leaf


Sessile - means "sitting" or "resting on the surface” but essentially means without a petiole (as in some leaves), or without a pedicel (as in some flowers and fruits). It is a characteristic of plant parts which have no stalk. Flowers or leaves are borne directly from the stem or peduncle, lacking a petiole or pedicle. Stalkless flowers, as in a spike with sessile flowers attached directly at the base

Sexual propagation - deliberate, directed reproduction of plants using seeds or spores. (See Asexual propagation)

Sexual reproduction - reproduction of plants through a sexual process involving cell division

Shear - cut back a plant (as opposed to selective pruning or deadheading). Often used to regenerate plants with many small stems, where dead-heading would be too time consuming

Sheath - basal portion of the leaf surrounding the grass stem. In grass plants, it is usually split with overlapping edges

Shoot - stem, one season’s branch growth that possesses leaves. The bud scale scars (ring of small ridges) on a branch mark the start of a season’s growth

Shoot meristem - apex of a shoot where cells actively divide to provide more cells that will expand and develop into the tissues and organs of the plant. Also called apical meristem

Short-day plant - plant requiring more than 12 hours of continuous darkness to stimulate a change in growth, e.g., a shift from the vegetative to reproductive phase. (See Long-day plant, Day-neutral plant)

Shot-hole - clean-edged,  roughly round to oval holes in leaves resulting from the dropping out of the central dead areas of spots

Shoulder ring - one of the ridges around the base of a branch where it attaches to a trunk or to another branch. (See Collar)

Shrub - woody plant that has multiple stems and branches at or near the ground and grows to a height of 3 to 12 feet, relatively small, especially when compared to trees

Side-dress - apply fertilizer to the soil around a growing plant

Sieve tube - food-conducting cell in the phloem

Sign - part of a pathogen seen on a host plant; the physical evidence of something that has attacked a plant

Signal word - indication of toxicity on pesticide labels. Pesticides labeled “caution” are the least toxic, those labeled “warning” are more so, and those labeled “danger” are the most toxic

Silt - type of soil particle that is intermediate in size between sand and clay

Simple bud - bud containing either leaf or flower primordia, but not both

Simple layering - method similar to tip layering, except that the stem behind the end of the branch is covered with soil and the tip remains above ground

Simple leaves - leaf blades consisting of one unit

Simple metamorphosis - type of insect development involving three stages: egg, nymph, and adult. The nymph usually resembles the adult. (See Complete metamorphosis)

Sinuate - having a pronounced wavy margin

Sinus - indentation of a leaf. Sinuses alternate with lobes

Siphonaptera - major order of insects that have two pairs of wings, or are wingless, and piercing-sucking mouthparts as adults and chewing mouthparts as larvae (fleas)

Slicing - penetration of turf in a vertical plane by a series of solid flat tines.

Slime flux - type of ooze specific to trees where the fermentation of plant fluids creates pressure

Slime mold - 'primitive' class of of soil-, litter-, or bark-dwelling fungi called Myxomycetes. They are saprophytic fungi that live on dead organic matter, such as wood mulch, and appear in several different colors and usually go unnoticed until the conspicuous spore-producing phase in spring or early summer after soaking rains

Slit seeder - gasoline-powered machine that slices even rows into the soil, and drops grass seed directly into those rows to improve seed-soil contact. Slit seeders are most typically used to apply seed over an existing lawn, where mature grass or weeds may get in the way of the new seed

Slow-release fertilizer - pellets manufactured with a coating of wax or other insoluble or very slowly soluble material to provide a predictable, slow release of the encapsulated materials (fertilizer). In most cases this material must be converted into a plant-available form by soil microorganisms

Smut - black masses of spores produced by fungi that may form on stems, ears of corn, etc. A specific type of fungus that grows in the grain heads

Soft pinch - remove only the succulent tip of a shoot, usually with the fingertips

Soft rot - water soaked appearance of cells that don’t get enough oxygen

Softwood cuttings - cuttings taken from soft, succulent, new spring growth of deciduous or evergreen species of woody plants

Soil - outer, weather layer of the earth's crust that has the potential to support plant life. It is a natural, biologically active mixture of weathered rock fragments (inorganic particles), organic matter, microorganisms, water, and air at the earth’s surface

Soil horizons - soil horizon is a layer generally parallel to the soil crust, whose physical characteristics differ from the layers above and beneath. Each soil type usually has three or four horizons. Horizons are defined in most cases by obvious physical features, chiefly color and texture

Soil management - practices used in treating a soil, which may include various types of tillage and production systems

Soil salinity - measure of the total soluble salts in a soil

Soil solution - solution of water and dissolved minerals found in soil pores

Soil structure - arrangement of individual soil particles or their aggregates

Soil texture - how coarse or fine a soil is. Texture is determined by the proportions of sand, silt, and clay in the soil

Soilless mix or substrate - components used in potting mixes that are not true soils, such as vermiculite, perlite, peat, bark, sand, gravel, sphagnum moss used in container growing mixes but no real soil

Solitary flower - plant that forms a stalk that bears a single flower, such as a tulip

Soluble salt - mineral (salt) often remaining in soil from irrigation water, fertilizer, compost, or manure applications

Sonic repelle - sonic wave-emitting unit said to disrupt the activities of small mammals or insects but not proven to be effective

Sooty mold - common name given to a condition that is not truly a disease, but a black coating on leaves, branches and fruit made up of a fungal growth that is usually dark colored and powdery-like, giving it the name sooty mold. These fungi are saprophytic, that is, they do not feed on live plant tissue, but rather thrive on insect secretions, known as honeydew, that are high in sugars

Sori - cluster of sporangia borne on the underside of a fern frond

Species - group of individual plants interbreeding freely and having many (or all) characteristics in common

Species-specific - limited to effecting one species or a certain group of species

Specific epithet - second word in a Latin binomial. Sometimes called trivial name

Specimen - individual plant with outstanding characteristics (leaves, flowers, or bark), generally used as a focal point in a landscape

Spike - flower cluster of an indeterminate (unlimited number) raceme of sessile flowers attached to the floral axis with the oldest flowers at the base

Spikelet - diminutive type of spike inflorescence found in grasses

Spiking - penetration of turf in a vertical plane by series of solid round tines

Spiller - plants placed along the edge of a combination container to spill or trail out of the pot

Spines - modified leaves, leaflets, petioles or stipules that appear as sharp-pointed, woody structures. Examples include: blackberries or greenbriar

Spiracles - circular tubes in the exoskeleton of insects that allow air into the trachea. In an insect’s respiratory system, tracheal tubes deliver oxygen directly to tissues

Split complementary - use of a pure color and a color from either side of its complementary counterpart

Spongy parenchyma - lower layer of cells in the mesophyll

Spore - reproductive body of a fungus or other lower plant, containing one or more cells. (2) A bacterial cell modified to survive in an adverse environment. (3) The reproductive unit of ferns

Sport - see Mutation

Spot treatment - apply a pesticide to a small section or area of a crop

Spreading - plants that grow low and spread along the ground, rooting at nodes along the stem

Sprig - stolon or rhizome used to establish turf

Spur - short, stubby stems common on fruit trees such as apples and pears. These spurs produce the flower buds

Stamen - male part of the flower consisting of the anther in which pollen is produced and a slender filament that holds the anther in a position favorable for pollen dispersal

Staminate flower - flowers in which only the stamens (male reproductive parts) with no pistil (female reproductive parts) are present, also called imperfect because they lack the pistil

Standard - plant pruned so that it consists of a single bare vertical stem, atop which a shaped mass of foliage, usually globular, is maintained

Stem cutting - section of a stem prepared for vegetative propagation; forms adventitious roots on the stem

Stem galls - swellings, usually woody, on stems

Sterile - material that is free of disease organisms (pathogens), as in potting medium. (2) A plant that is unable to produce viable seeds

Stigma - receptive surface on a pistil that receives pollen

Stippled - covered with white dots or flecks

Stipules - leaflike appendages often found on either side of the base of the petiole; they may subtend the leaf, but they are not actual parts of the leaf


Stock (rootstock) - lower part of a graft

Stolon - above-ground creeping stem that can produce roots and shoots at each node. This horizontal stem can be either fleshy or semi-woody

Stoloniferous - producing or bearing stolons

Stoma, stomate, (stomata plural) - pore or opening on the surface of a leaf (epidermis) herbaceous stems through which gases (water vapor, carbon dioxide, and oxygen) are exchanged. This pore is an opening into a leaf that is formed by specialized epidermal cells on the underside (and sometimes upper sides) of the leaf

Stomatal complex - term is also used collectively to refer to an entire stomatal complex, both the stomatal pore itself and its accompanying guard cells

Stone fruit - fleshy fruit, such as a peach, plum, or cherry, usually having a single hard stone that encloses a seed. Also called a drupe

Strain - variation within a cultivar or variety

Stratification - storing of seeds at low temperatures (chilling) under moist conditions to break physiological dormancy or rest. This method mimics the conditions a seed might endure after it falls to the ground in the autumn and goes through a cold winter on the ground

Style - located on a pistil, a tube connecting the stigma and the ovary

Stylet - nematode’s lance like or needlelike mouth-part. Used to puncture and feed from plant cells

Subapical meristem - aids in formation of shoots and flowering stalks

Subspecies - major division of a species, more general in classification than a cultivar or variety

Succession - progression of a plant community to a stable mixture of plants

Succession planting - practice of planting new crops in areas vacated by harvested crops; Several smaller plantings made at timed intervals

Succulent - leaf textures that are fleshy, soft, and thickened in texture; modified for water storage

Succulent leaves - water storage structures characteristic of plants in and and semiarid regions

Sucker - shoot or stem that originates underground from a plant’s roots or trunk, or from a root- stock below the graft union. (See also Reversion growth)

Summer annual - annual plant in which the seed germinates in the spring, and the plant develops, matures, and produces seed by the end of the growing season

Summer oil - light refined horticultural oil used during the growing season to control insect pests and diseases

Sun scald - winter or summer injury to the trunk or leaves of plants caused by hot sun and fluctuating temperatures. Typically, sun scalded bark splits and separates from the trunk

Supplemental Water - water added through irrigation using drip irrigation, soaker hoses, or other non-natural means

Surfactant - see Additive

Susceptibility - condition of a plant in which it is prone to the damaging effects of a pathogen or other factor

Sustainable gardening - gardening practices that allow plants to thrive with minimal inputs of labor, water, fertilizer, and pesticides

Suture - line of junction of contiguous plant parts

Swale - low place in a tract of land, usually moister than the adjacent higher land. A valley-like intersection of two slopes in a piece of land

Symbiotic - mutually beneficial

Symptom - plant’s response to an attack by animal or pathogen; a visible reaction of a plant to disease such as wilting, necrosis, abnormal coloration, defoliation, fruit drop, abnormal cellular growth, or stunting

Synthetic fertilizer - chemically created fertilizers, mainly from inorganic materials

Synthetic pesticide - chemically formulated pesticide, mainly from inorganic sources

Systemic - spreading internally throughout the plant

Systemic pesticide - pesticide that moves throughout a target organism’s system to eliminate it


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