HERBS - the basics

The Anatomy Of Irises

What kinds of plants are they? First of all, the foliage is grass like with the same sort of parallel veining you find in grasses, lilies and orchids. Next, you notice that the sword like leaves don't seem to have stems, but usually rise from ground level. In actuality, the rhizomes, bulbs and corms of irises are modified stems.

The tripartite look of the flowers, with three standards and three falls, is a singular characteristic of irises, lending grace and beauty in combination with spectacular colors that are hard to beat. These botanically significant traits will help you better understand irises.

Irises are angiosperms, the scientific term for flowering plants. There are some 250,000 flowering plants in the world, according to current thought. The parallel veining in the leaves and flower parts that are in multiples of three are clear signs that irises are monocotyledons. The word "monocotyledon" means that these plants have single seed leaves, the third significant clue for monocots. Another important characteristic of monocotyledons is that the vascular bundles - the circulatory systems of plants - are distributed throughout the plant tissue, unlike the ring arrangement of vascular bundles in dicotyledons. Lilies (Lilium spp.) and daylilies (Hemerocallis spp.) also are well-known monocots of the ornamental-garden world. Monocotyledons as a group are divided into those that have petaled flowers like the irises and those that don't, like the plants of the Gramineae or grass family.

Within these vascular bundles are the tissues that carry water and nutrients up from the roots to the green foliage. This tissue is called the xylem. The phloem is the vascular tissue that carries carbohydrates, the products of photosynthesis, down from the foliage to the roots, rhizomes and bulbs. Green plants are the only organisms that can manufacture nutrients, using sunlight, water and carbon dioxide to produce simple carbohydrates. That is why green plants are placed at the bottom of the food chain. All other life, plant and animal alike, can trace its survival back to green plants used as foods.

Angiosperms fall into two groups, the monocotyledons described above and dicotyledons, the term for those plants having two seed leaves. Unlike monocots with their three-part flowers, the flower parts of dicots develop in fours or fives or multiples of fours and fives. Dicotyledon plants have netlike leaf veining and vascular bundles that are arranged in rings. This group is well represented in the garden by the flowering shrubs, fruit trees, roses, zinnias and many others.

The three-part flowers of irises form singly or severally on branches of the flower stalks. Each iris flower has three uprights (standards) and three falls, the later, more correctly, the sepals. They usually lie flat or turn down toward the stem. One or more flower buds are enclosed within two modified leaves that are often called spathes. The spathes may be papery or thicker in texture.

The spathes vary in color, texture, shape and size from species to species. Therefore, they can be important in the identification of irises. They can also be of value in trying to guess the heritage of unknown irises, since spathe characteristics may be among the more obvious distinctions that are carried through from ancestral plant parents.

Iris flowers differ widely in appearance and in size, as well as in the relative sizes of their parts. Not only do they come in a dazzling array of colors, color combinations and color patterns, but they also, from species to species throughout the genus Iris, have an overall iris look while exhibiting many variations on the theme.

The major flower parts include the standards (petals), falls (sepals), perianth tube, stamens (male organs) and the pistils (female organs), including stigma, style and ovary. The characteristics of species and cultivars are reflected most positively through the colors and color patterns of the standards and falls. Together, the standards and falls make up what is collectively called the perianth. The stamens are the pollen-bearing male organs of the iris flower. They are made up of the anthers at the top, which bear the pollen grains, and the filaments that are the stems of the stamens. In the iris flower, the stamens are located under the style and facing the claw of the branches.

In the iris flowers, the ovary is inferior, that is, it lies at the bottom of the flower. The perianth tube surrounds the pistils and connects the ovaries with the perianth. The ovary is the ovule-bearing structure that is at the base of the flower. Fertilization of the ovules occurs when the tubes of the pollen grains grow through the style into the ovary. The style connects the ovary with the style, which is positioned opposite the falls. The style branches have two little "wings" called crests that shelter the stigma. The stigma is the ridge or lip located at the top of the undersurface of the style branch, and it is here that pollen grains must be deposited to begin the process of pollination.

Iris flowers, like the flowers of other plants, have evolved over millions of years with a single purpose: to develop seeds and thus ensure the future of the parent plant. The form, flower color and often the aroma combine to attract insects and thus increase the chances of pollination and subsequent development of seeds. In the case of irises, the beard or crest, the signal and the structure of the falls attract insects and provide the pollinators with a landing platform. When the insects reach forward and into the nectar-bearing tube of the flowers, they brush by the pollen-carrying anther, picking up pollen grains. Visiting another flowers to take more nectar, they brush by the wet stigma to which the pollen grains adhere. Today's powerful microscopes help botanists study pollen grains, the apertures of which vary in important ways and often are part of the basis for iris classification.

While the foliage of all of the irises is usually sword-shaped with parallel veining, there is a great deal of variety in the many species. Iris leaves often have a waxy coating or bloom that is grayish in color. The texture of the leaves varies from species to species, from thick to thin, from rigid to pliable and from soft to hard. The fans of leaves are vertical and each leaf blade usually is broader at the base.

Folds on the inward edges of the leaves act as sheaths to hold the leaves tightly together, with the base of each leaf nesting inside the leaf behind it. While the flat, sword-shaped leaf is the most common type in the Iris genus, some species have leaves that are nearly cylindrical or square or channeled in cross section. If the leaves are channeled, the underside may have a pronounced keel.

Irises can be divided into two main groups according to the types of underground structures they have. The first group has fibrous roots plus modified stems called rhizomes that usually grow horizontally at or near the soil surface. This group includes all of the bearded irises plus the beardless Siberian, Pacific Coast, Louisiana, spuria and Japanese irises.

The second group of irises has fibrous roots plus bulbs, another type of modified stem that consists of fleshy scale leaves that surround a bud plus a short stem. Included within this group are the reticulated, Xiphium (often called Dutch, Spanish or English irises) and scorpio or juno irises. Juno irises are bulbous and also have thick, fleshy storage roots, these being the characteristic that distinguishes them from the Xiphium irises.

There is one species that falls between the two main groups, being neither rhizomatous nor bulbous. That is Iris nepalensis, which is, as you might guess from the species name, native to the temperate regions of the Himalayan Mountains, including the country of Nepal. Both rhizomes and bulbs are root like storage structures that make it possible for plants to buffer vagaries of climate.

Both rhizomes and bulbs store nutrients and moisture, then give them up to the rest of the plant when needed. The bulbs have differing coats (tunics), depending upon the iris group they are in. Bulb coatings maybe reticulated (netted), papery or thick and leathery. The fibrous roots may be plentiful or scanty depending upon the iris type. They may be thick like those of tall bearded irises or thin and even wiry like those of spuria irises. Some irises, including the evansia irises of damp woodlands, are able to spread by means of slender horizontal stems called stolons that grow out from the main plant near the soil surface.

The rhizomatous irises can be further divided according to the type of feature they have along the center of their falls. The bearded or pogon irises all have a distinctive pattern of long hairs along the top of the basal half of the falls called the beard. Other irises have crests and still others have merely a smooth ridge. Often there are signals on the falls, patches of color that contrast with the rest of the falls. The signals serve as guides to help orient pollinating insects, directing them toward the nectar source along a path where their bodies will brush against the anthers and stigmas.

The seedpods or capsules are based on three parts, just as are the flowers, and they differ greatly in specific size and shape. Botanists make use of seeds, seedpods and flowers in classifying irises, especially the beardless species. Some seedpods are short while others are long. Some are stocky while others are slim. Some are quite round while others show their three sections distinctly. Some iris seedpods are strongly ribbed. Iris seeds may be rough or smooth. Some iris seeds have loose, shiny coatings. The seeds of aril irises, including Oncocycluses, Regelias and Hexapogon irises, have fleshy, creamy-white appendages at one end.


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