Life on our planet would not be possible, much less enjoyable, without plants. They provide food either directly or indirectly to all animal life. Their leaves create oxygen, and their roots grip the soil and prevent erosion. Their branches shade and cool the ground, and they beautify our surroundings with their interesting shapes, colors, textures, and scents. Botany is the scientific study of plants. This chapter will help you understand how plants are classified, the names of their structural and reproductive components, how they grow, including the physiological processes, and how plants are influenced by environmental factors. A deep understanding of these topics will help you in diagnosing plant problems and recommending appropriate management techniques.
Plumeria rubra grows as a spreading shrub or small tree to a height of 2–8 m (5–25 ft) and similar width. It has a thick succulent trunk and sausage-like blunt branches covered with a thin grey bark. The branches are somewhat brittle and when broken, ooze a white latex that can be irritating to the skin and mucous membranes. The large green leaves can reach 30 to 50 cm (12 to 20 in) long and are arranged alternately and clustered at the end of the branches. They are deciduous, falling in the cooler months of the year. The flowers are terminal, appearing at the ends of branches over the summer. Often profuse and very prominent, they are strongly fragrant, and have five petals. The colors range from the common pink to white with shades of yellow in the center of the flower. Initially tubular before opening out, the flowers are 5–7.5 cm (2–3 in) in diameter, and only rarely go on to produce seed – 20-60 winged seeds are contained in a 17.5 cm (7 in) pod.
Some forms in cultivation are hybrids between this species and Plumeria obtusa; these have rounded rather than pointed leaves and are less likely to be deciduous. The white and yellow cultivar “Singapore” flowers all year round in Hawaii.
Taxonomy – Plant/Plumeria classification
More than 350,000 different types of plants live on our planet. With new species being discovered regularly and others becoming extinct, that number changes constantly (Kew Gardens). Scientists group plants that share common characteristics to make it easier to identify and study plants. This type of organization based on the characteristics of organisms is called taxonomy.
Plumeria rubra was one of the many species first described by the father of taxonomy Carl Linnaeus, and appeared in the 1753 edition of Species Plantarum. Its specific epithet is derived from the Latin ruber “red”. The epithets acuminata, acutifolia, and lutea are seen, but these are invalid.
The hierarchy of classification is as follows:
- Kingdom: Plantae
- Phylum: Angiosperms
- Class: Eudicots
- unranked: Asterids
- Order: Gentianales
- Family: Apocynaceae
- Tribe: Plumerieae
- Genus: Plumeria
- Species: P. ruba
- Binomial Name: Plumeria Ruba
- Variety or Cultivar
Kingdom Plantae is divided into two types of land plants:
Phylum Gymnosperm—Gymnosperm comes from the Greek word “gymnospermos,” which means “naked seed.” Gymnosperms produce seeds like angiosperms, but those seeds are not contained in a ripened ovary; they form at the tips of scales or leaves that are sometimes modified into cones. Conifers are the largest group of gymnosperms, and they bear seeds in cones. Some gymnosperms have fleshy coats or tissues surrounding seeds (yews and ginkgoes, for example).
Phylum Angiosperm—Angiosperms are flowering plants that produce seeds contained in a fruit (a ripened ovary). Fruits have evolved to attract animals that help to disperse seeds. In addition, some fruits decompose, adding organic matter to the soil that the new plant can use to grow. Angiosperms comprise the vast majority of land plants. Flowering plants can be further divided into two classes: monocots and dicots. Some of their differences are listed in Table 3–1. We will talk more about monocots and dicots when we discuss plant anatomy and reproduction.
Table 3–1. Differences between Monocots and Dicots
|Class Monocots||Class Dicots|
|Embryo with single cotyledon||Embryo with two cotyledons|
|Pollen with single furrow or pore||Pollen with three furrows or pores|
|Flower parts in multiples of three||Flower parts in multiples of four or five|
|Major leaf veins parallel||Major leaf veins netted|
|Stem vascular bundles scattered||Stem vascular bundles in a ring|
|Roots that are adventitious||Roots that develop from radicle|
|Secondary growth is absent||Secondary growth often present|
|Examples: asparagus, corn, ginger, grasses, iris, lilies, onions, palms, tulips||Examples: apples, beans, cabbage, elms, oaks, peppers, peas, potatoes, roses, spinach, squash|
What’s in a name?
Plumeria Common Names
In Mexico the common name is Cacaloxochitl or Suchitl. The name comes from nahuatl and means Crow’s flower. The common name in Australia is ‘frangipani’, although ‘plumeria’ is used in the United States. Other common names are ‘red frangipani’, ‘common frangipani’, ‘temple tree’, or simply ‘plumeria’. The term meliais a Hawaiian one. The common name ‘frangipani’ comes from an Italiannoblefamily, a sixteenth-century marquess of which invented a plumeria-scented perfume. In the Cook Islands, it is known as Tipani. It is grown extensively in southern and western parts of India, where it is named champa or a derivative thereof such as chaaphaa, champige etc. In Cambodia it is given the names châmpéi krahâ:m (also romanised as krahom, meaning ‘red’), or châmpéi slük sruëch, while the French terms for the species is frangipanier à fleurs rouges.
All plants have a Latin scientific name consisting of two parts, the genus and the species. This naming method is called binomial nomenclature, and it is the only consistent and dependable way to reference plants. Common names, while popular, have several shortcomings:
- Some plants have multiple common names and may be called by different common names in different states and regions. For example, the evergreen shrub Kalmia latifolia is called mountain laurel, mountain ivy, Virginia ivy, mountain kalmia, and kalmia laurel. The deciduous tree Liquidambar stryacifluahas been called American sweetgum, sweet-gum, red gum, star-leaved gum, or alligator-wood.
- The same common name is sometimes applied to several different plants. For example, tea or tea plant could be Camellia sinensis, Chenopodium ambrosioides (also known as Dysphania ambrosioides), Ilex glabra, or others.
- Some plants may have no common name.
With binomial nomenclature, it is clear you are referring to a specific plant. The first part is the generic name, which describes the genus, and the second part is the species. For the sweet gum tree Liquidambar styraciflua, the genus is Liquidamar and the species is styraciflua. A genus is a group of related species. Genera, the plural of genus, are grouped into families, families into orders, and on up the hierarchy of taxonomic classification. The scientific name is capitalized and underlined or written in italics. In some cases, the genus may be abbreviated to the first letter followed by a period. For example, Euonymus americanus, strawberry bush, may be abbreviated as E. americanus.
The second part of the scientific name is called the specific epithet. The epithet describes the species, which is the next level of classification. Individual plants within a species have many common characteristics, yet are distinct from other species in the same genus. Specific epithets are often derived from a description of a flower or leaf, the area where the plant was discovered, or the plant’s habitat; sometimes epithets also honor a person. Epithets are written in lowercase letters and are underlined or italicized. (Table 3–2).
Table 3–2. Examples of epithets and their translations
|sylvatica||of the forest|
There are several small, inexpensive dictionaries on the market and websites that give the pronunciation of and a short definition for many Latin terms. Understanding the translation makes it easier to remember the scientific name. There are even sites on the Internet that spell botanical Latin names out phonetically. See the “For More Information” section at the end of this chapter for suggestions.
Two additional terms used in identifying plants are “variety” and “cultivar.” A variety is a naturally occurring subset of a species with distinctive features that are true to type, meaning that when propagated sexually, through seeds, the offspring have the same characteristics as the parent plant. The varietal name is also an epithet, added after the name of the species and preceded by the abbreviation “var.” For example, Cercis canadensis var. alba is a white flowering redbud that was discovered in the wild. “Alba” means white, and seeds from this variety grow into plants that have white flowers.
A cultivar, as the name suggests, is a variety that has been cultivated by humans. Cultivars are selected for one or more unique traits and are usually propagated vegetatively to maintain these traits. If a new type of tomato were developed by crosspollination in a breeding program, it would be a cultivar. A cultivar name follows the species name and is enclosed in single quotation marks; each word begins with a capital letter. For example, Cornus florida ‘White Cloud’ is White Cloud flowering dogwood. It is not necessary to use the single quotes if the word “cultivar” precedes the cultivar name.
Plants vary with respect to their growth and developmental cycles. Annuals complete their entire life cycle, from seed germination to seed production, and die in one growing season. Examples of annuals are corn, beans, marigolds, and zinnias. Biennials complete their life cycles in two growing seasons. In the first season, they start from seeds and produce vegetative structures and food storage organs. During the winter, a hardy evergreen rosette of leaves persists. During the second season, they flower, produce fruits and seeds, and die. Some examples of biennials are carrots, hollyhocks, celery, beets, and onions. Annuals and biennials are herbaceous plants, meaning their above ground tissue dies back and they do not have a persistent above ground woody stem.
Perennials live for more than two growth seasons, up to several years, decades, or even centuries. After they reach maturity, they can produce flowers and fruit each year. Perennial plants can be either herbaceous or woody plants. Herbaceous perennials die down to the ground each winter and grow new stems from their persistent root system each spring. Several herbaceous perennials that do not tolerate cold are treated as annuals. Many bedding plants are perennial in the wild but are treated as annuals in the garden. Perennial woody plants have stems that live through the winter.
Plumeria Trees are perennial woody plants that usually have one main trunk and normally are more than 15 feet tall at maturity. Plumeria trees can grow to be much taller when planted in the ground or in their natural environment.