Sessility (botany)

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The perennial wildflower Trillium cernuum possesses three leaves that are sessile at the top of the stem. Trillium cernuum 1-eheep (5098010914).jpg
The perennial wildflower Trillium cernuum possesses three leaves that are sessile at the top of the stem.

In botany, sessility (meaning "sitting", used in the sense of "resting on the surface") is a characteristic of plant parts (such as flowers and leaves) that have no stalk. [1] [2] Plant parts can also be described as subsessile, that is, not completely sessile.

A sessile flower is one that lacks a pedicel (flower stalk). A flower that is not sessile is pedicellate. For example, the genus Trillium is partitioned into two subgenera, the sessile-flowered trilliums (Trillium subg. Sessilium) and the pedicellate-flowered trilliums.

Sessile leaves lack petioles (leaf stalks). A leaf that is not sessile is petiolate. For example, the leaves of most monocotyledons lack petioles.[ citation needed ]

The term sessility is also used in mycology to describe a fungal fruit body that is attached to or seated directly on the surface of the substrate, lacking a supporting stipe or pedicel. [3]

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<i>Trillium</i> Genus of flowering plants

Trillium is a genus of about fifty flowering plant species in the family Melanthiaceae. Trillium species are native to temperate regions of North America and Asia, with the greatest diversity of species found in the southern Appalachian Mountains in the southeastern United States.

Panicle Term used in botany to describe a branching of flower heads

A panicle is a much-branched inflorescence. Some authors distinguish it from a compound spike inflorescence, by requiring that the flowers be pedicellate. The branches of a panicle are often racemes. A panicle may have determinate or indeterminate growth.

Raceme Unbranched, indeterminate type of inflorescence bearing pedicellate flowers along its axis

A raceme or racemoid is an unbranched, indeterminate type of inflorescence bearing pedicellate flowers along its axis. In botany, an axis means a shoot, in this case one bearing the flowers. In indeterminate inflorescence-like racemes, the oldest flowers are borne towards the base and new flowers are produced as the shoot grows, with no predetermined growth limit. A plant that flowers on a showy raceme may have this reflected in its scientific name, e.g. Cimicifuga racemosa. A compound raceme, also called a panicle, has a branching main axis. Examples of racemes occur on mustard and radish plants.

Frond collection of leaflets on a plant

A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the large leaves of cycads, as well as palms (Arecaceae) and various other flowering plants, such as mimosa or sumac. "Frond" is commonly used to identify a large, compound leaf, but if the term is used botanically to refer to the leaves of ferns and algae it may be applied to smaller and undivided leaves.

<i>Commelina</i> Genus of flowering plants

Commelina is a genus of approximately 170 species commonly called dayflowers due to the short lives of their flowers. They are less often known as widow's tears. It is by far the largest genus of its family, Commelinaceae. The Swedish taxonomist Carl Linnaeus of the 18th century named the genus after the two Dutch botanists Jan Commelijn and his nephew Caspar, each representing one of the showy petals of Commelina communis.

<i>Chlorophytum comosum</i> Species of flowering plant

Chlorophytum comosum, usually called spider plant but also known as spider ivy, ribbon plant, and hen and chickens is a species of evergreen perennial flowering plant. It is native to tropical and southern Africa, but has become naturalized in other parts of the world, including western Australia. Chlorophytum comosum is easy to grow as a houseplant; variegated forms are the most popular.

Peduncle (botany) Stalk of a plant bearing an inflorescence or solitary flower

In botany, a peduncle is a stalk supporting an inflorescence or a solitary flower, or, after fecundation, an infructescence or a solitary fruit. The peduncle sometimes has bracts at nodes. The main axis of an inflorescence above the peduncle is the rachis. There are no flowers on the peduncle but there are flowers on the rachis.

<i>Trillium ovatum</i> Species of flowering plant

Trillium ovatum, the Pacific trillium, also known as the western wakerobin, western white trillium, or western trillium, is a species of flowering plant in the family Melanthiaceae. It is found in western North America, from southern British Columbia and the tip of southwestern Alberta to central California, east to Idaho and western Montana. There is an isolated population in northern Colorado and southern Wyoming.

<i>Trillium undulatum</i> Species of flowering plant

Trillium undulatum, commonly called painted trillium, painted lady, or trille ondulé in French, is a species of flowering plant in the bunchflower family Melanthiaceae. It is also known as smiling wake robin or striped wake-robin. The specific epithet undulatum means "wavy", which refers to the wavy edges of the flower petals. The plant is found from Ontario in the north to northern Georgia in the south and from Michigan in the west to Nova Scotia in the east.

Petiole (botany) The stalk holding a leaf to its stem

In botany, the petiole is the stalk that attaches the leaf blade to the stem, and is able to twist the leaf to face the sun. This gives a characteristic foliage arrangement to the plant. Outgrowths appearing on each side of the petiole in some species are called stipules. Leaves with a petiole are said to be petiolate, while leaves lacking a petiole are called sessile or apetiolate. For the use of the term in entomology see petiole

<i>Trillium sessile</i> Species of flowering plant

Trillium sessile, known as toadshade, sessile trillium, sessile-flowered wake-robin, and toad trillium, is a perennial spring wildflower native to the central part of the eastern United States and the Ozarks. Toadshade can be distinguished from other Trillium species by its single, foul smelling, stalkless, flower nestled in the middle of its three bracts. The bracts are sometimes, but not always mottled with shades of light and dark green. The specific epithet comes from the Latin word sessilis which means low sitting, referring to its stalkless flower.

Pedicel (botany) Structure connecting flowers or fruit to the main stem of a plant

A pedicel is a stem that attaches a single flower to the inflorescence. Such inflorescences are described as pedicellate.

This page provides a glossary of plant morphology. Botanists and other biologists who study plant morphology use a number of different terms to classify and identify plant organs and parts that can be observed using no more than a handheld magnifying lens. This page provides help in understanding the numerous other pages describing plants by their various taxa. The accompanying page—Plant morphology—provides an overview of the science of the external form of plants. There is also an alphabetical list: Glossary of botanical terms. In contrast, this page deals with botanical terms in a systematic manner, with some illustrations, and organized by plant anatomy and function in plant physiology.

<i>Trillium stamineum</i> Species of flowering plant

Trillium stamineum, the twisted trillium, also known as the Blue Ridge wakerobin, is a species of flowering plant in the family Melanthiaceae. It is native to the southeastern United States, in Alabama, Mississippi and Tennessee. Its natural habitat is calcareous woodlands.

This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary of leaf morphology. For other related terms, see Glossary of phytopathology and List of Latin and Greek words commonly used in systematic names.

Leaf Photosynthetic part of a vascular plant

A leaf is the principal lateral appendage of the vascular plant stem, usually borne above ground and specialized for photosynthesis. The leaves, stem, flower and fruit together form the shoot system. Leaves are collectively referred to as foliage, as in "autumn foliage". In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves are flattened and have distinct upper and lower surfaces that differ in color, hairiness, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves are mostly green in color due to the presence of a compound called chlorophyll that is essential for photosynthesis as it absorbs light energy from the sun. A leaf with lighter-colored or white patches or edges is called a variegated leaf.

<i>Trillium petiolatum</i> Species of flowering plant

Trillium petiolatum, the Idaho trillium, also known as the long-petioled trillium or round-leaved trillium, is a species of flowering plant in the family Melanthiaceae. It is native to the northwestern United States, in Idaho, Oregon, and Washington. The type specimen for this species was gathered by Meriwether Lewis in 1806 along the Clearwater River during the return trip of the Lewis and Clark Expedition.

Whorl (botany)

In botany, a whorl or verticil is an arrangement of leaves, sepals, petals, stamens, or carpels that radiate from a single point and surround or wrap around the stem or stalk. A leaf whorl consists of at least three elements; a pair of opposite leaves is not called a whorl.


In plant morphology, a cataphyll is a reduced, small leaf. Many plants have both "true leaves" (euphylls) which perform the majority of photosynthesis, and cataphylls that are modified to perform other specialized functions.

Trillium viride, commonly called the wood wakerobin, is a species of flowering plant in the family Melanthiaceae. It is found in the central United States, in certain parts of Missouri and Illinois. The specific epithet viride means "youthful" or "fresh-green", an apparent reference to the color of the plant's flower petals. For this reason, it is also called the green trillium, not to be confused with other green-flowered trilliums such as T. viridescens and the green form of T. sessile, both of which are found in Missouri.


  1. Beentje, H.; Williamson, J. (2010). The Kew Plant Glossary: an Illustrated Dictionary of Plant Terms. Royal Botanic Gardens, Kew: Kew Publishing.
  2. Hickey, M.; King, C. (2001). The Cambridge Illustrated Glossary of Botanical Terms. Cambridge University Press.
  3. Ulloa, Miguel; Halin, Richard T. (2012). Illustrated Dictionary of Mycology (2nd ed.). St. Paul, Minnesota: The American Phytopathological Society. p. 575. ISBN   978-0-89054-400-6.