Flowering Plants

The Western Red Lily (or Prairie Lily).
Bonnie Galenzoski

The flowering plants, or Angiosperms as botanists refer to them, are a vast cosmopolitan assemblage dominating plant life on earth today and comprised of approximately 250,000 species. Not only do their attractive flowers and overall beauty aesthetically enrich our lives, but flowering plants are vital to human existence as the biosphere’s primary producers and sources of our sustenance, shelter, and other necessities. The name angiosperms originated from a combination of the Greek words angeion (vessel) and sperma (seed): angiosperms can thus be defined as seed-bearing vascular plants, with true flowers having the ovules (immature seeds) borne enclosed in a hollow ovary. While the cones of gymnosperms, the other seed-bearing plants, are basically equivalent to angiosperm flowers, their ovules (seeds) are borne naked (i.e., uncovered) on surfaces of cone scales. Angiosperms also differ from gymnosperms in having vessels (large tubes) in their conducting (vascular) system, and an endosperm (nutriment for the embryo in the seed) developing after rather than before fertilization. Non-seed bearing vascular plants such as ferns, horsetails, and club-mosses, and non-vascular plants such as mosses and liverworts, have sporangia (spore-cases) in which single-celled spores develop, to be eventually released and dispersed, and to germinate on suitable substrate to grow into new plants.

Needle-and-thread grass.
Dean Nernberg (Environment Canada, Canadian Wildlife Service)

Angiosperms evidently originated from a cycad-like line of gymnosperms as early as the Jurassic Period, but did not appear on the world scene in sizable numbers until the early-mid Cretaceous Period about 112 million years ago, when already quite diverse. Their early evolutionary history has posed some riddles owing to a fragmentary fossil record. By the end of the Cretaceous Period, about 65 million years ago, angiosperms had overwhelmingly replaced gymnosperms as the dominant plants on earth. They successfully adapted to and colonized most available habitats as they spread over the face the earth.

Angiosperms have evolved into an amazing array of life-forms, ranging in size from minute floating plants 1-2 mm in diameter (e.g., Watermeal, Wolffia spp.) to tall trees reaching heights of 100 m for some Australian eucalyptus species, although seldom over 30 m for Saskatchewan hardwood trees. In general life-form, angiosperms are broadly categorized as either woody plants (trees, shrubs, and some vines) with persistent aerial stems, or herbaceous (non-woody) plants with aerial stems dying back to ground level at the end of each growing season. Trees are the larger woody plants, often defined as over 3.5 m tall, with mostly single main trunks, in contrast to the shorter and usually multi-stemmed shrubs. Herbaceous plants are categorized by their longevity as: annuals, living for a single growing season; biennials, living for two seasons to flower the second; and perennials, living for several to many seasons and producing new flowering shoots from their bases each season.

Flowers are the distinctive reproductive structures of angiosperms. They vary greatly in size, from microscopic in duckweeds to nearly a metre broad in some tropical blossoms. A typical complete angiosperm flower consists of a receptacle (enlarged tip of flower stalk) that bears four basic sets of floral parts. These floral sets, from the outermost inward, are sepals (collectively calyx), petals (collectively corolla), stamens (collectively androecium), and pistils (collectively gynoecium). The reproductively essential floral parts are stamens (male structures) and pistils (female structures). An ovary containing the ovules forms the basal part of a typical pistil, with a stalk-like style atop the ovary and terminated by a pollen-receptive stigma. Stamens typically consist of stalk-like filaments bearing terminal anthers containing pollen sacs in which pollen is produced. The often conspicuous and colourful petals of flowering plants seemingly evolved for the purpose of attracting pollinating insects. Sepals, the outermost floral parts, are characteristically leaf-like and generally function to envelop and protect the immature flower in bud stage, and later lend support for the other floral parts.

Pollination is the transfer of pollen from the anthers of stamens to the stigmas of, mostly, other flowers. This is usually accomplished by insects and other animals, less frequently by wind, or occasionally by water. Upon their conveyance onto a stigma, pollen-grains form pollen-tubes that grow downward through the style to the ovary and thence to the ovules within, where male sperm cells are inserted to fertilize the contained eggs. A fertilized egg develops into an embryo within the ovule, which eventually matures as a seed, and its enveloping ovary as the fruit. After dispersal and often a dormant period, seeds may germinate in suitable sites to produce seedlings that grow into new plants.

Much variation exists among angiosperm flowers with respect to the basic parts, including number, size, fusion, texture, colour, the presence or absence of whole floral sets, and the flower-symmetry. Complete flowers have all four floral sets, while incomplete flowers are missing one or more whole sets of parts. Both functional stamens and pistils are present in bisexual (or perfect) flowers, but the absence of either results in unisexual (or imperfect) flowers. Monoecious plants have both staminate (male) and pistillate (female) flowers present on the same individuals (e.g., birches and cattails); but they are borne on different plants in dioecious plant groups, resulting in separate male and female individuals in a population (e.g., willows and poplars). Those flowering plants that are pollinated by insects tend to display more conspicuous corollas (e.g., lilies, orchids, roses, milkweeds, snapdragons), while wind-pollinated plants generally have quite inconspicuous and often much-reduced flowers (e.g., birches, maples, goosefoots, grasses, sedges). While the term wildflowers often seems used to refer only or mainly to the more conspicuously flowered herbaceous plants in nature, the flowering plants include all species with true flowers, whether these are conspicuous or not, and whether the plants are herbaceous or woody. The many diverse character combinations of floral structures and other plant attributes among angiosperms serve to distinguish the numerous species and higher groupings.

Common (or vernacular) names for flowering plants originated independently in many places over the world, resulting in a multiplicity of names differing among regions, cultures, and languages. As the science of botany developed, professional botanists, to avoid confusion, established a worldwide, standardized, scientific naming system governed by internationally accepted rules, the International Code of Botanical Nomenclature (ICBN). The scientific names for plant species are in Latin form and consist of two parts: a genus name and a species epithet.

In modern plant classifications, the flowering plants are recognized as a major group within the Plant Kingdom, usually at the division or subdivision level, and comprised of two large subgroups, the monocotyledons and dicotyledons. Approximately a quarter-million species of angiosperms exist worldwide, which are grouped by botanists into about 300 plant families of various sizes. Globally, the largest flowering plant families in number of included species are: the orchid family (Orchidaceae), with over 17,000 species; the aster family (Asteraceae), with about 13,000 species; the legume family (Fabaceae), with about 12,000 species; and the grass family (Poaceae), with about 10,000 species.

Listed for Canada are 141 naturally occurring families of flowering plants, including 891 genera and 4,006 species. The largest angiosperm families in Canada in number of included species are: the aster family, with 525 species; the grass family, with 312 species; the sedge family (Cyperaceae), with 358 species; the rose family (Rosaceae), with 207 species; the legume family, with 192 species; and the mustard family (Brassicaceae), with 177 species. About 78% of Canadian species are native (i.e., indigenous or original), and 22% naturalized (i.e., exotic introductions becoming naturally established).

Recognized for Saskatchewan are 127 families of flowering plants, including 600 genera and 1,625 species. The largest families in Saskatchewan in number of included species are: the aster family, with 240 species; the grass family, with 197 species; the sedge family, with 150 species; the mustard family, with 78 species; and the legume family, with 56 species. Following closely, with about 50 species each, are the rose family, goosefoot family (Chenopodiaceae), and pink family (Caryophyllaceae). The sedge genus, Carex, with 168 species, is the largest in Saskatchewan in number of species and is distantly trailed by: the willow genus, Salix, with 31 species; the milkvetch genus (Astragalus), with 24 species; the rush genus, Juncus, with 22 species; and the violet genus, Viola, with 20 species. About 80% of Saskatchewan’s flowering plants are native, and 20% are introduced and naturalized.

It is impossible to describe the whole spectrum of Saskatchewan flowering species in a brief account. They range from the many brightly coloured wildflowers and less conspicuously flowered plants of prairies, woodlands, and byways to sundry trees and shrubs, aquatic plants, sedges and grasses. Possibly surprising to those who do not envisage such plants at this latitude, there are 10 species of carnivorous (insect-eating) plants, 25 orchid species, and three cactus species native to Saskatchewan.

It is noteworthy that flowering plants are particularly well represented among Saskatchewan’s official emblems, including not only the official provincial flower, the western red lily (Lilium philadelphicum var. andinum), but also the provincial tree, the white birch (Betula papyrifera), and the provincial grass, the needle-and-thread (Heterostipa comata).

Vernon L. Harms

Further Reading

Harms, Vernon L. 2003. Checklist of the Vascular Plants of Saskatchewan, and the Provincially and Nationally Rare Native Plants in Saskatchewan. Saskatoon: University of Saskatchewan Extension Press; Scoggan, H.J. 1978. The Flora of Canada, Part 1. Ottawa: National Museum of Natural Sciences; Willis, J.C. 1973. A Dictionary of the Flowering Plants and Ferns, 8th edition. Cambridge: Cambridge University Press.