Table of Contents
Areoles are the distinctive feature of cacti, and identify them as a separate family from other succulent plants. Areoles give rise to spines or, on certain cacti, small, detachable glochids which are an additional form of protection. The areoles on cacti are clearly visible. They generally appear as small light to dark colored bumps, out of which grow clusters of spines.
Areoles represent highly specialised branches on cacti. They are believed to have evolved as vestigial leaves of cacti were modified into spines over time. Thus, the branches became reduced to buds which give rise to the spines. This means that as cacti adapted and evolved to the desert climate, over time they got rid of branches and leaves, which were converted into areoles and spines to protect the plants, and to reduce water loss.
Some cacti lack spines on their areoles, but instead, (as said above) utilise small, detachable glochids which resemble small, sharp splinters and are very difficult to remove from the skin.
A branch is a part of a woody plant such as a tree, shrub, or vine. It is any woody structural member that is usually connected to but not part of the central trunk. A branch supports the terminal twigs, which in turn support the leaves.
Branches may be oriented in any direction from horizontally to vertically, but usually have bark similar to the upper trunk (whereas twigs are often marked different to the bark).
A large or main branch is sometimes called a limb or bough, while very small branches are called branchlets or twigs.
In botany, a drupe is a type of fruit in which an outer fleshy part (exocarp, or skin; and mesocarp, or flesh) surrounds a shell (the pit or stone) of hardened endocarp with a seed inside. These fruits develop from a single carpel, and mostly from flowers with superior ovaries. The definitive characteristic of a drupe is that the hard, lignified stone (or pit) is derived from the ovary wall of the flower.
Other fleshy fruits may have a stony enclosure that comes from the seed coat surrounding the seed. These fruits are not drupes.
Some flowering plants that produce drupes are coffee, jujube, mango, olive, most palms (including date, coconut and oil palms), pistachio and all members of the genus Prunus, including the almond (in which the mesocarp is somewhat leathery), apricot, cherry, nectarine, peach, and plum.
The term stone fruit can be a synonym for “drupe” or, more typically, it can mean just the fruit of the Prunus species.
Drupes, with their sweet, fleshy outer layer, attract the attention of animals as a food, and the plant population benefits from the resulting dispersal of its seeds. The endocarp (pit or stone) is often swallowed, passing through the digestive tract, and returned to the soil in feces with the seed inside unharmed; sometimes it is dropped after the fleshy part is eaten.
Many stone fruits contain sorbitol, which can exacerbate conditions such as irritable bowel syndrome and fructose malabsorption.
The coconut is also a drupe, but the mesocarp is fibrous or dry (in this case, called a husk), so this type of fruit is classified as a simple dry fruit, fibrous drupe. Unlike other drupes, the coconut seed is unlikely to be dispersed by being swallowed by fauna, due to its large size. It can, however, float extremely long distances across oceans.
In an aggregate fruit composed of small, individual drupes, each individual is termed a drupelet. Bramble fruits (such as the blackberry or the raspberry) are aggregates of drupelets. The fruit of blackberries and raspberries comes from a single flower whose pistil is made up of a number of free carpels.
(Gr. “inside” + “fruit”), is a botanical term for the inside layer of the pericarp (or fruit), which directly surrounds the seeds. It may be membranous or thick and hard, such as in cherries, plums, and apricots.
An evergreen plant is a plant that retains its leaves all year round, with each leaf persisting for more than 12 months. This contrasts with deciduous plants, which completely lose all their foliage for part of the year, becoming bare and leafless.
Leaf persistence in evergreen plants may vary from only just over a year (shedding the old leaves very soon after the new leaves appear), up to a maximum of 45 years (in one species of Pine). However, very few species show leaf persistence of over 5 years.
(Gr. “outside” + “fruit”), is a botanical term for the outermost layer of the pericarp (or fruit). The epicarp, or exocarp, forms the tough outer skin of the fruit. The exocarp is sometimes called the epicarp.
Glochids are tiny, almost invisible barbed hairs found on the areoles of some cacti and other plants. Cactus glochids easily detach from the plant and become lodged in the skin, causing irritation upon contact with the tufts that cover some species, each tuft containing hundreds of tiny barbs.
A hesperidium (plural hesperidia) is a fleshy berry with a tough, leathery rind. Oranges and other citrus fruits are common examples.
The peel contains volatile oil glands in pits. The fleshy interior is composed of separate sections, called carpels, filled with fluid-filled vesicles that are actually specialised hair cells.
An inflorescence is a group or cluster of flowers on a branch of a plant. In botany the term refers to the way individual flowers are arranged on the plant, in which single or multiple flowers develop on the same stem. There are two fundamental terms used to describe the nature of inflorescences:
- Determinate – the first flowers of the inflorescence to open are at the top end of inflorescence or terminal. The top flower blooms first.
- Indeterminate – the first flowers to bloom are the ones at or near the bottom of the inflorescenes, that is the first flowers start blooming at the bottom of the stem or inside a cluster of flowers.
A leaf is an above-ground plant organ specialised for photosynthesis. For this purpose, a leaf is typically flat (laminar) and thin, to expose the cells containing chloroplast (chlorenchyma tissue, a type of parenchyma) to light over a broad area, and to allow light to penetrate fully into the tissues. Leaves are also the sites in most plants where respiration, transpiration, and guttation take place. Leaves can store food and water, and are modified in some plants for other purposes. The comparable structures of ferns are correctly referred to as fronds.
(Gr. “middle” + “fruit”), is a botanical term for the middle layer of the pericarp (or fruit). It is often fleshy forming the bulk of the fruit.
The Pericarp is the botanical term for the tissue surrounding a seed that develops from the ovary wall of the flower. Generally the pericarp is the fruit making body. This includes many types of fruits including nuts, but does not include a few fruits like figs. In some cases, such as the acorn, the pericarp becomes dry and hard, forming a shell around the seed. In fleshy fruits the pericarp is typically made up of three distinct layers: the exocarp (the outside or the peel), the mesocarp (the middle layer), and the endocarp (the inner layer).
The petiole is the small stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the leaf.
Phyllodes are modified petioles. In some plants, the petioles become flattened and widened, while the leaf itself becomes reduced or vanishes altogether. Thus the phyllode comes to serve the purpose of the leaf.
Sessile means “without a stalk”, as in flowers (pedicel) or leaves (petiole) that grow directly from the stem.
A shrub or bush is a horticultural rather than strictly botanical category of woody plant, distinguished from a tree by its multiple stems and lower height, usually less than 6 m tall. A large number of plants can be either shrubs or trees, depending on the growing conditions they experience. Small, low shrubs such as lavender, periwinkle and thyme are often termed subshrubs.
Spines are the ends of branches or leafs, that have been modified into rounded, hard structures with sharp ends. They are often also called thorns, which are reduced, sharp pointed stems.
Spines are used by plants to protect themselves from herbivores. Some plants with spines and animals that feed on them, have co-evolved in response to each other, with some plants having very long spines and the animals that feed on those species having long tongues to reach past the spines to feed on the leaves.
The spines of different cactus are leafs that have been completely transformed. The sharp Long thorns of the hawthorn, the needles of a cactus, and the prickles of a shrub like the rose are all spines. Although spines generally serve as a passive defense mechanism, in some species they can be hollow and contain poisonous substances that cause lasting pain or even paralysis, and in others, may be barbed and detach readily, sticking to whatever brushes against them.
Botanists use several terms somewhat loosely when referring to spine- or needle-like structures on plants; however, the following differences are typically distinguished:
- Prickle – a sharp outgrowth from the epidermis, also called an emergence and usually involving some subdermal tissue as well.
- Spine – a modified stipule or sharp branchlet found in a leaf axil or on the margin of a leaf.
- Thorn – Sharp outgrowth from a stem other than at a node; a modified stem.
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence (flowers), cones or other stems etc. The internodes act as spaces that distance one node from another. The term shoots is often confused with stems, shoots generally refer to new fresh plant growth and does include stems but also to other structures like leaves or flowers. The other main structural axis of plants is the root. In most plants stems are located above the soil surface but some plants have underground stems.
Stems have four main functions which are:
- Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.
- Transport of fluids between the roots and the shoots.
- Storage of nutrients.
- The production of new living tissue. The normal life span of plant cells is one to three years. Stems have cells that annually generate new living tissue.
A stipule refers to outgrowths borne on either side of the base of a leafstalk (the petiole). A pair of stipules is considered part of the anatomy of the leaf of a typical flowering plant, although in many species the stipules are inconspicuous or entirely absent (and the leaf is then termed exstipulate).
Stipules are morphologically variable and might appear as glands, scales, hairs, spines, or laminar (leaf-like) structures.
Stratification is the storing of seeds at low temperatures under moist conditions in order to break dormancy.