GNETALES: CHARACTERISTICS, HABITAT, CARE, DISEASES - BIOLOGY - 2025

Gnetales corresponds to an order of gymnosperm vascular plants whose family Gnetaceae is represented by a single genus (Gnetum) that groups some 43 species, many of which are climbers.

The leaves of plants of the genus Gnetum are very similar to those of angiosperm plants. They develop two leaves at the nodes, are wide and have a venation with a midrib that gives rise to lateral secondary veins towards the edges of the leaves.

Gnetum ula. Source: Dinesh Valke from Thane, India

A distinctive feature of this order and related orders within gymnosperms is that the plants have vessels in the xylem. This allows a more efficient pathway for the movement of water, and it could be assumed that, especially the species of the genus Gnetum, were the plants that would have given rise to the evolution of angiosperms.

These plants are abundant in Asia and have some representatives in America. The wood of the arboreal species is hard and at night they emit a foul odor. There is no record of Gnetum species that they are usable in dendrochronology.

Regarding the uses of these plants, some are used to make ropes, others produce edible seeds and some species are useful in Chinese medicine as anti-asthmatics.

In addition, tree species due to their rapid growth and high resistance to wind (even cyclones), are important in environmental regeneration plans and in arboriculture.

characteristics

Appearance

Most of the species belonging to the order gnetales are tree climbing lianas, very characteristic of tropical forests. Some representatives of this order are trees almost 10 m high, with large leaves and very similar to the leaves of angiosperm plants.

The stems of the species of the genus Gnetum are less visible than those of the order Ephedrales, since in the latter, leaves are produced on branches or short shoots, which allows their stem to be easily observed.

Leaves

The leaves of plants of the genus Gnetum are very similar to those of angiosperm plants, especially dicotyledonous ones. These species have two leaves at the nodes, are wide and have a venation with a middle vein from which secondary lateral veins derive towards the leaf margins (reticulated venation).

The gnetal leaves look like dicot angiosperm leaves. Source: Dinesh Valke from Thane, India

Reproductive structures

The reproductive structures of the gnetals (as is characteristic of gymnosperms), are within strobili or cones. Most of these species are dioecious, meaning that a plant produces pollen or produces seeds but not together.

In the case of the seed-producing structures they are known as megasporangiate strobili, and in those of the pollen they are known as microsporangiate strobili. In both, the two strobili have bracts arranged in the opposite direction from the axillae, and short fertile shoots grow from these.

The strobili in this genus are compact or may be elongated by nodes and internodes. Two fused bracts that enclose a microsporangiophore are formed in male strobili (microsporangiate). There are usually two microsporangia that are seen separately at the end of each sporophyll.

Male strobilus in Gnetum sp. Source: Kembangraps

On the other hand, in megasporangiate strobili the structure called dome or collar produces 8 to 10 ovules, and each ovule has three integuments around it.

In the genus Gnetum there are no archegonia present and, at the micropylar end of the female gametophyte, there is an area without divisions but with several nuclei. At this point, each nucleus behaves like an egg cell and joins the nucleus of the male gamete, thus forming a zygote.

The other male nucleus joins a female nucleus and from this fusion the endosperm is formed. In this case, there is a double fertilization although the development of the embryo does not take place the same as in angiosperms.

The pollen grains are moved by the wind until they reach the ovules where they are attached to them through the pollen drop and from there they pass to the micropylar tube. This pollination process, together with the formation of seed, can last a year.

Seeds

The seeds are shiny in appearance and similar to yellowish drupes.

The seeds of some gnetal species are edible. Source: Hariadhi

Taxonomy

- Kingdom: Plantae

- Phylum: Tracheophyta

- Class: Gnetopsida

- Order: Gnetales

On the other hand, they also contain lignans that are substances of the guaiacyl-syringil type, while Gnetum parviflorum has demethylcoclaurin hydrochloride which is used as an antiasthmatic in Chinese medicine.

Care

Floor

Gnetals can grow in a wide range of soil textures. These can be sandy, clayey, silty, or combinations thereof.

Irrigation

The species of the genus Gnetum must remain in soils with good drainage, because they are intolerant to waterlogging. On the contrary, they are quite tolerant to drought for several months.

In this sense, these plants can easily develop only with the water coming from the rain, or be watered once a week.

Light

Gnetal species normally grow under direct sun exposure, but have a high tolerance for shade.

Temperature

These plants grow in places with tropical characteristics such as an average annual temperature between 22 and 30 ° C and a minimum temperature of 12.8 ° C.

Gnetum gnemon. Source: Alex Lomas

Diseases

The literature referring to the gnetales order does not offer sufficient data on the diseases or pests that can affect the species of this group.

References

1. Gnetaceae. 2019. In: Plant diversity reference guide. Faculty of Exact and Natural Sciences and Surveying (UNNE). Pages 54-56.
2. Jáuregui, D., Benítez, C. 2005. Morphological aspects and foliar anatomy of the Gnetum L. (gnetaceae-gnetophyta) species present in Venezuela. Acta Botánica Venezuelica 28 (2): 349-368.
3. Gifford, EM 2018. Gnetophyte. In: Encyclopedia Britannica. Taken from: britannica.com
4. The Gymnosperm Database. 2019. Gnetum. Taken from: conifers.org
5. Manner, H., Elevitch, C. 2006. Gnetum gnemon (gnetum). In: Species Profiles for Pacific Island Agroforestry. Taken from: traditionaltree.org
6. Catalog of Life: 2019 Annual Checklist. Order Gnetales. Taken from: catalogueoflife.org