- Saccate. Pouch-like
- Sagittate. Lobe pointed and oriented downward or inward in relation to petiole or midrib; sinus depth variable; margins variable
- Sagittiform. Triangular-ovate with two straight or slightly incurved basal lobes
- Salient, Porrect, or Projected. Pointed outward, usually said of teeth
- Salverform. Trumpet-shaped; with slender tube and limb nearly at right angles to tube
- Samara. A winged, dry fruit
- Samaracetum. An aggregation of samaras, as in Liriodendron
- Sapromyiophily. Pollinated by carrion or dung flies
- Sarcocauly. Fleshy stems
- Sarcous. With the seed coat fleshy
- Scaberulent. Approaching scabrous
- Scabridulous. Minutely scabrous
- Scabrous. Having a harsh surface
- Scale. Small, non-green leaf on bud and modified stem; small, scarious to coriaceous flattened bodies within the perianth, as in the Cyperaceae and Asteraceae. Scale Leaf - Small, usually appressed and imbricate; e.g., Juniperus, Thuja
- Scape. A naked flowering stem with or without a few scale leaves, arising from an underground stem
- Scapose. With a solitary flower on a leafless peduncle or scape, usually arising from a basal rosette
- Scarious. Thin and dry, appearing shriveled
- Scarred. With old leaf base, stipular and/or branch scar regions
- Schizocarp. Separated body, as in separating fruits (achenes, berries, carcerules, follicules, mericarps, nutlets, samaras), splitting apart at maturity
- Sclerocauly. Hard, dryish stems
- Sclerous. Hard
- or Lentiginous. Scurfy or Lentiginous With exfoliating scaly incrustations
- Seasonally. Occurring during a seasonal cycle, or each season
- Secund or Unilateral. Flowers or other structures on one side of axis
- Seed. A matured ovule. Seed Coat - Outer protective covering of seed
- Segment. The ultimate division or unit of a dissected fern leaf
- Semataxis. Arrangement of semaphylls (petals, sepals, tepals), primarily advertising (pollinator attracting) in function
- Semicarpous. With ovaries of adjacent carpels partly fused, stigmas and styles separate
- Semicraspedodromous. With a single primary vein, the secondary veins branching just within the margin, one branch from each terminating at the margin and the other forming a marginal loop and joining the superadjacent secondary vein
- Sepal. A calyx member or segment; a unit of the calyx
- Sepaliferous. Most frequently at the base of sepals
- Sepaloid. Sepal-like in shape, texture and/or color
- Septal. At the junction of the septa in the ovary
- Septate. Divided by internal partitions into locules or cells
- Septum or Dissepiment. Partition. Septicidal Capsule - One that dehisces longitudinally through the septa, as in Penstemon
- Sericeous. With long, silky trichomes, usually appressed
- Serotinal. Opening late; appearing in late summer
- Serrate. Saw-toothed; teeth sharp and ascending, but cut 1/16-1/8 distance to midrib or midvein
- Serrated. Cut into sawlike teeth
- Serrulate. Diminutive of serrate, but cut to 1/16 distance to midrib or midvein
- Sessile. Without a petiole or petiolule
- Seta. A hair-like extension of the leaf, as in homophyllous species of Selaginella
- Setose, Setaceous. Having setae or bristlelike trichomes
- Sheath. Any more or less tubular portion of the leaf surrounding the stem or culm, as in the Poaceae
- Sheathing. Having tubular structure enclosing stem below apparent insertion of blade or petiole
- Shining, Nitid, or Laevigate. Lustrous, polished
- Shrub. A much-branched woody perennial plant usually without a single trunk
- Silicle. A dry, dehiscent fruit derived from two or more carpels that dehisce along two sutures and which has a persistent partition after dehiscence and is as broad as, or broader, than long
- Silique. A silicle type fruit that is longer than broad
- Simple. Not composed of more than one anatomically or morphologically equivalent unit
- Sinistrorse. Rising helically from left to right, a characteristic of twining stems
- Sinuate. Long horizontal curves in the body of the structure parallel to the central axis
- Siphonostele. A stele having vascular tissue in the form of a hollow cylinder, with a central pith
- Soboliferous. With loosely clumped shoots arising some distance apart from rhizomes or under ground suckers
- Solenostele. A siphonostele having phloem both internal and external to the xylem
- Solitary. One-flowered, not an inflorescence
- Sorosis. Fruits on a common axis that are usually coalesced and derived from the ovaries of several flowers, as in Morus
- Sorus. A cluster of sporangia
- Spadix. Unbranched, indeterminate inflorescence with flowers embedded in the rachis
- Spathe. An enlarged bract enclosing an inflorescence
- Spathulate or Spatulate. Oblong or obovate apically with a long attenuate base
- Spatulate. Foliate, erect embryo with variable cotyledons, thin to thick and slightly expanded to broad
- Spherical. With multi-dimensional radial symmetry
- Sphingophily. Pollinated by hawk moths and nocturnal lepidoptera
- Spiculate. With crystals in or on the surface
- Spike. Unbranched, indeterminate, elongate inflorescence with sessile flowers
- Spikelet or Locusta. A small spike; the basic inflorescence unit in grasses and sedges
- Spine. Sharp-pointed petiole, midrib, vein, or stipule
- Spinose or Pungent. Acuminate but coriaceous and stiff
- Spiral. Twisted like a corkscrew
- Spirolobal. With incumbent cotyledons folded once
- Spongy. Cellular; sponge-like
- Sporangiophore. The umbrella-shaped sporangium-bearing unit of the strobilus, as in Equisetum
- Sporangium. A spore case
- Sporocarp. A hard, nut-like structure containing the sporangia in heterosporous ferns
- Sporophyll. A spore bearing leaf
- Spotted. The color disposed in small spots
- Spur. A short shoot on which flowers and fruits or leaves are borne; a tubular or pointed projection from the perianth
- Squamose. Having coarse scales
- Squarrose. Usually sharply curved downward or outward in the apical region, as the bracts of some species of Aster
- Stamen. Male sporophyll within the flower; floral organ that bears pollen in angiosperms
- Staminal. Most frequently at base of filament
- Staminate or Male. With stamens only in the flower
- Staminodial. Frequently entire structure is nectariferous
- Staminodium. Sterile stamen, may be modified as a nectary or petaloid structure. Staminal Disc - A fleshy, elevated cushion formed from coalesced staminodia or nectaries
- Standard, Banner, or Vexillum. The upper, usually wide petal in a papilionaceous corolla
- Stele. The central primary vascular system of the stem and associated tissues delimited from the cortex by endodermis and pericycle, Delimited from the cortex by endodermis and pericycle
- Stellate. Star-shaped
- Stem. A supporting and conducting organ usually developed initially from the epicotyl and growing upward
- Stereomorphic. Flowers 3-dimensional with basically radial symmetry; parts many or reduced, and usually regular; e.g., Narcissus, Aquilegia
- Stigma. Pollen-receptive portion of pistil
- Stipe, Podogyne, Carpopodium. Basal stalk. Stipe Bundles - The vascular bundles of the fern petiole
- Stipellate. With stipels
- Stipels. Paired scales, spines, or glands at the base of petiolule
- Stipulate. With stipules
- Stipules. Paired scales, spines, glands, or blade-like structures at the base of a petiole. Stipular Scar - A mark indicating former place of attachment of stipule
- Stolon. Runner or indeterminate, elongate, above ground propagative stem, rooting at the tip producing new plants. Underground Stolon - A determinate, elongate, underground propagative stem with long internodes forming a bulb or tuber at the tip
- Stoloniferous. Bearing stolons; sarmentose
- Stomate. Opening or pore in leaf epidermis; intercellular space between two guard cells
- Stomium. Lip cell region of a fern sporangium
- Striate. With longitudinal lines
- Strict. Stiff and rigid
- Strigillose. Diminutive of strigose
- Strigose. Covered with sharp, coarse, bent trichomes usually with a bulbous base
- Striped. Longitudinal stripes of one color crossing another
- Strobilus. Stem with short internodes and spore-bearing appendages; a cone
- Strombiform. Elongate snail-shaped
- Strophiolate. With elongate aril or strophiole in the hilum region
- Style. Attenuated, non-ovule-bearing portion of pistil between stigma and ovary
- Stylocarpellous. With a style and without a stipe, the normal carpel
- Stylocarpepodic. With a style and stipe
- Stylopodic. With a stylopodium or discoid base, as in the Apiaceae
- Subacrocaulous. With branches at or near tip of main stem
- Subapical. At one side near apex of ovary
- Subbasal. Near the base
- Subbasicaulous. With branches at or near base of main stem
- Subbasifixed. Anther attached near its base to apex of filament
- Suberous. Corky
- Subglabrate. Almost glabrous
- Subglobose. Almost round or spherical
- Submersed. Beneath the surface of the water
- Submersicaulous. With submersed stems
- Subtend. To stand below and close to
- Subterminal. Near the apex
- Subterranean or Hypogeous. Below the surface of the ground
- Subulate. Very narrow and tapering; awl-shaped; linear
- Sucker Shoots. Shoots that develop from adventitious buds on old stumps or roots, usually after cutting or injury, which have elongate internodal lengths and intervals
- Suffrutescent. Woody basally, herbaceous apically
- Sulcate. With longitudinal grooves
- Summer Annual. Germinating in spring or early summer and flowering and fruiting in late summer or early fall, then dying
- Superior. Other floral organs attached below ovary
- Supervolute. With lamina with one edge tightly enrolled and with the other loosely enrolled covering the first, loosely convolute
- Supine. Prostrate, with parts oriented upward
- Suprafoliar. On the stem above the leaves, as in the Arecaceae
- Suprarhizous. On top of the root
- Surcarpous. With fruits on surface of ground
- Surcurrent. Extending along stem upward from leaf base
- Surficial or Epigeous. Upon or spread over the surface of the ground
- Syconium. A syncarp with the achenes borne on the inside of a hollowed-out receptacle or peduncle, as in Ficus
- Syleptic Shoots. Abnormal shoots that develop from lateral buds before they have reached maturity
- Sympetalous. With fused petals
- Sympatric. Collocated, together
- Sympodial. Branching without a main axis but with many, more or less, equal laterals
- Synantherous. With leaves and flowers appearing at same time
- Syncarpous. With fused carpels
- Syncotyly. Cotyledons coalesced, forming a funnel or trumpet
- Syngenesious. With fused anthers
- Synovarious. With ovaries of adjacent carpels completely fused, styles and stigmas separate
- Synsepalous. With fused sepals
- Synstylovarious. With ovaries and styles of adjacent carpels completely fused, stigmas separate
- Syntropous. With radicle pointing toward hilum