Gymnosperms & Angiosperms: Evolution and Diversity

• Lecture 8 covers the evolution and the diversity of Gymnosperms and Angiosperms.
• Seeds are the primary means of reproduction and dispersal for both Gymnosperms and Angiosperms.
• Seeds are reproductively superior to spores due to advanced embryonic development.
• Seeds contain an abundant food supply and a protective seed coat.
• Seeds changed plant evolution around 400 MYA.
• Gymnosperms became dominant in terrestrial ecosystems by the Mesozoic era (~250MYA) as water was no longer required for reproduction.
• Reduced gametophytes, heterospory, ovules, and pollen are common to all seed plants.
• Gametophytes of seed plants develop within the walls of spores, retained within tissues of the parent sporophyte.
• Gymnosperms are also Tracheophytes, like ferns, club mosses, and horsetails.
• Gymnosperm means "naked seed."
• Naked seeds, not enclosed in fruits, distinguish gymnosperms from other plants.
• Gymnosperms are cone-bearing plants
• Gymnosperms lack enclosed chambers (ovaries) for seeds, thus ovules and seeds develop on specialized leaves called sporophylls.
• Ginkgo, cycads, and conifers are examples of gymnosperms.
• Most gymnosperms are evergreens, with needle-shaped leaves.
• The vascular tissue of gymnosperms features tracheids for water conduction and support in the xylem.
• Seeds in gymnosperms are on cones
• Features like vascular systems with seeds either exposed or on cones and wind-borne pollen grains distinguish gymnosperms from bryophytes and ferns.
• Monoecious plants have both male and female reproductive organs on the same individual.
• Diecious plants have male and female reproductive organs on separate individuals.

Phylum Coniferophyta

• The most familiar gymnosperms are conifers (cone bearers) like pines, spruces, firs, cedars and sequoias redwoods..
• Conifers produce wood, bark, needles, and seeds in cones.
• Most conifers are monoecious.
• Forest fires allows female cones will burst open and release seeds.

Other Gymnosperms

• Other lesser known gymnosperm examples are Ginkgos of phylum Ginkgophyta are imported from East Asia and used in US city parks for their pollution resilience.
• The sole member of phylum Ginkgophyta is Ginkgo biloba which is a deciduous, dioecious species.
• Female ginkgo trees produce seeds directly on branches.

Phylum Cycadophyta

• Cycads (Sago Palms) that look like palms or ferns.
• Cycads are dioecious, but reproduce with pollen and seeds in conelike structures.
• Few cycad members are still in existence, as they used to be numerous.

Gnetophytes

• Gnetophytes consist of three genera: Gnetum, Ephedra, and Welwitschia.
• Gnetophytes are unique among gymnosperms and share traits with angiosperms.
• Gnetophytes have vessel elements in their xylem and cone clusters resembling flower clusters.
• Life cycle details resemble those of angiosperms.
• Welwitschia only lives in African deserts.
• Gnetae has little cones at the base of the leaves.

Review of Terms

• Haploid refers to single set of chromosomes which can be in sperm or egg cell, spore and in the gametophyte
• Diploid refers to 2 of each chromosome and can be found in the zygote, seed and the sporophyte

Dry Land Adaptations

• Obtaining an adequate supply of water, development of true roots conduct water to upper parts of plant
• Means of physical support are conducting tissues in stem called wood
• Means of getting sperm to egg without water has led to development of wind-blown pollen grains and pollen tube to carry sperm to egg
• Need of protective structure for developing zygote, a development of seed for protecting and nourishing embryo
• Less available carbon dioxide has led to the development of stomata (openings on leaves)
• Must withstand wider range of temperature, wind, and humidity has led to the development of waxy cuticle on the leaves

Angiosperms

• Angiosperms of phylum Anthophyta are also known as phylum Magnoliophyta.
• Angiosperms are Vascular plants that produce enclosed flowers with seeds inside of a fruit.
• Angiosperms are the most diverse and successful group of plants.
• Flowers may contain sepals, petals, stamens and carpels
• Everything since the ferns is included in Tracheophytes because they all have vascular systems for transport and plant organs which include true roots, stems, and leaves.
• Ovules are enclosed within an ovary which after fertilization become seeds and the ovary develops into fruit
• Angiosperms are flowering plants
• The angiosperm life cycle is: sporophyte generation is dominant, gametophytes are reduced in size and are nutritionally dependent on sporophyte generation, are Heterosporous and within the flower produce microspores.
• Angiosperm megaspores, egg cell and central cell with two polar nuclei participate in fertilization.
• Angiosperms achieve double fertilization, resulting in a diploid zygote and a triploid endosperm.
• Distinguishing characteristics of phylum Anthophyta (Angiosperms) are flowers and fruits.
• Angiosperm means covered seed (seed in a vessel and/or fruit).