What is a gymnosperm?

Gymnosperm plants make up a group of vascular plants , that is, with internal structures that conduct substances such as water and mineral salts, and that are distinguished by producing seeds, but not producing flowers .

Origin

Plants with seeds (structures that contain the fertilized ovule that later develops into an embryo) arose on Earth approximately 360 million years ago. The low temperatures due to the glaciations and the droughts at the end of the Carboniferous period caused the extinction of many of the predominant plants, which reproduced by spores (cells capable of developing a new organism without fusing with another cell). This gave way to plants with seeds, which kept embryos protected and with the possibility of dispersing to optimal environments for their growth.

Characteristics

Gymnosperms have, like other plants, leaves, roots and stems. Many plants in this group have needle-shaped leaves, a characteristic that allows them to survive in ecosystems where humidity is scarce, such as those where the climate is temperate or cold, or where the soil is sandy.

Another distinctive feature of gymnosperms is that their seeds are naked, that is, they are not protected within an ovary that will later form a fruit. Instead, they develop into scale-like structures, which in many species form a cone. Pines, for example, produce two types of cones: the male ones, which house pollen grains and are located at the ends of the branches, and the female ones, which house the ovules, which are larger than the male ones and are covered by scale-like structures.

Lifecycle

Taking a pine tree as an example, the adult tree is known as a sporophyte , because it contains sporangia , that is, spore-producing structures located in cones. If the cones are male, these spores develop male gametophytes , that is, regions that produce gametes, which in this case are spermatozoa contained in pollen grains. If the cones are female, the spores develop female gametophytes that produce gametes called ovules.

The wind carries pollen grains from the male cone to the female cone. There, the pollen grains release the male gametes, which join the ovules. The fertilized ovules form an embryo inside a seed. When the female cone is full of seeds it opens and the seeds are dispersed, fall to the ground and germinate to form new sporophytes.

Classification

Within gymnosperms there are four groups: gnetophytes, cycads, ginkgos and conifers.

• Gnetophytes are long-lived plants: between 1,500 to 2,000 years . Currently only 3 genera survive: Ephedra , with approximately 60 species that grow mainly in the American continent, Gnetum , with about 35 species of trees and vines abundant in tropical forests, and Welwitschia , with a single species exclusive to the deserts of southwestern Africa. .

• Cycads are plants that look like large ferns or low-lying palm trees . This group has a single genus called Cyca , with at least 160 species distributed mainly in ecosystems with a tropical climate. Cycas have variable lifespans, the longest-lived being a 5,000-year-old Australian specimen. 

• Ginkgos are plants represented by a single species called ginkgo biloba , whose small leaves are fan-shaped . The female trees are characterized by producing seeds similar to cherries, but with a very bad smell; the male trees are very resistant to contamination, which is why they are planted in large cities.

• Conifers are the most abundant and well-known gymnosperms . Examples of these plants are pines, firs, cypresses, and redwoods. Some conifers measure a few centimeters, while others exceed 50 meters in height. Due to the sharp shape of its leaves, which remain green all year round, they abound in cold latitudes and high altitudes, where humidity is very low.

Sources

Audesirk, T., Audesirk, G., Byers, B. Biology, Life on Earth with physiology . 9th edition. Pearson, San Francisco, 2011.

Biggs, A., Hagins, W.C., Holliday, W.G., Kapicka, C.L., Lundgren, L., Haley, A., Rogers, W.D., Sewer, M.B., Zike, D. Biology . Glencoe/McGraw-Hill., Mexico, 2011.

Curtis, H., Barnes, N.S., Schnek, A., Massarini, A. Biology . 7th edition. Editorial Médica Panamericana., Buenos Aires, 2013.