Asterids and Bryophytes: Plant Families, Traits and Life Cycles

Asterids: Families, Characteristics and Economic Importance

Clade asterids include the orders Ericales, Gentianales, Lamiales, Asterales and related groups. Representative families include Theaceae, Ericaceae, Sapotaceae, Ebenaceae, Actinidiaceae, Sarraceniaceae, Rubiaceae, Oleaceae, Apocynaceae, Scrophulariaceae, Lamiaceae, Apiaceae, Campanulaceae and Asteraceae.

Common traits of asterids include iridoids, tropane alkaloids, sympetalous (fused-petal) flowers, and ovules with a single integument. These angiosperms show the following features:

• Ericales: Family Ebenaceae includes important tropical fruit trees such as persimmon (Diospyros). Family Sapotaceae is important for industry and medicine; gum and argan oil are extracted from its members. Family Sarraceniaceae includes carnivorous plants. Family Actinidiaceae includes the kiwi (Actinidia). Family Ericaceae has simple leaves, solitary flowers, tetramerous or pentamerous actinomorphic flowers and androecium with bisexual (androgynous) flowers. Flowers are often insect-pollinated and have an urceolate (urn-shaped) corolla. The ovary may be superior or inferior, and the fruit is a soft fruit or capsule.
• Theaceae: Tropical and subtropical plants with alternate, simple leaves, actinomorphic, androgynous flowers and a superior ovary. Many species produce oil-rich seeds, such as tea (Camellia).
• Rubiaceae: Tropical herbs, shrubs and trees with simple, opposite leaves and cymose inflorescences. Flowers are pentamerous or tetramerous, actinomorphic and androgynous, with polycolpate pollen and a bicarpellate, bilocular, inferior gynoecium. Pollination is by insects or birds. The fruit is a capsule, drupe or berry. Economically important species include coffee and the source of quinine.
• Oleaceae: Found in Australia and Southeast Asia, with simple or pinnate, opposite leaves. Flowers are actinomorphic and androgynous, tetramerous, with a single or double perianth and a superior ovary.
• Scrophulariaceae: Found in temperate, subtropical and tropical zones. Flowers are solitary or in inflorescences, with a double, pentamerous perianth and androgynous flowers. Pollen is tricolpate and pollination is entomophilous. The fruit is a capsule. Many species contain medicinal saponin glycosides.
• Lamiaceae: Bilabiate (two-lipped) corolla, common in the Mediterranean region. Species produce antiseptic oils and wound-healing compounds. Flowers are zygomorphic, pentamerous and unisexual or androgynous, with four stamens in the androecium. Pollination is entomophilous and the fruit is a drupe.

Bryophytes: Structure, Life Cycle and Diversity

Bryophytes are terrestrial plants with non-lignified cells. They are poikilohydric, meaning they tolerate desiccation. They reproduce sexually by oogamy, with motile male gametes. Their life cycle is haplodiplontic, with a heteromorphic alternation of generations and gametophyte dominance. The sporophyte is independent in the early stage but remains physically attached to the gametophyte.

The haploid gametophyte produces gametes. Spores are unicellular, haploid products of meiosis, with a wall made of intine, exine and perine. The spore germinates into a filamentous protonema, which forms an apical cell bud that develops into the leafy gametophore. Mature gametophytes produce archegonia (female) and antheridia (male). After fertilization, the diploid sporophyte develops, living for a shorter time than the gametophyte. It is unbranched and produces one sporangium at the tip of a foot and capsule.

Bryophytes include three groups: hornworts (Anthocerotophyta), liverworts (Marchantiophyta) and mosses (Bryophyta).

Hornworts (Anthocerotes)

Hornworts evolved independently and have stomata. The gametophyte is dark green, with irregular, fleshy thalli that may bear tubercles. The sporophyte is a cylindrical capsule with a horn-like column that releases haploid spores and pseudoelaters from sporogenous tissue. Hornworts have chloroplasts with a pyrenoid, a reduced protonema, unicellular rhizoids, no hyaline rhizoids, unicellular gametangia without paraphyses and absent stomata. The sporophyte grows from an apical cell with simultaneous maturation. The seta is hyaline and elongates; spores are n or 2n.

Liverworts (Hepatics)

Liverworts have a gametophyte that is either thalloid or leafy, with two or three rows of leaves on the thallus. Some species have pores on the dorsal surface, ventral tissue for reserve storage, rhizoids and scales.

Mosses

Mosses are the largest group of bryophytes. The gametophyte has variable spores, a laminar or filamentous protonema, multiple rhizoids and a leafy gametophore. The sporophyte has a foot, a capsule with a cap, stomata in the capsule wall, central sterile tissue called the columella, a calyptra, and a capsule that opens through a peristome. The seta is surrounded by a cylindrical central hydroid strand with a cuticle. As the capsule matures, the seta elongates, and the operculum (lid) opens when the spores are mature.