Grass is some of the most diverse species of plant in the world and some of the most important in sustaining ecosystems. This week we’re looking at one particularly influential species of grass called Napier grass, among other common names. This species has become essential in sustaining agriculture around the globe.
Taxonomy and Evolution
Napier grass, also known as Uganda grass, napiergrass and elephant grass, (one of many species to go by this name), has two scientific names depending on what sources you use. According to the IUCN it has the scientific name Cenchrus purpureus although you might also see it referred to as Pennisetum purpureum, but for the purposes of this blog I will be referring to Napier grass as C. purpureus. As expected from its name Napier grass is a species of grass, officially the order Poaceae, which diverged from other grasses around 6 million years ago. This was around the time when global cooling led to the shrinking of the planet’s forests which opened the way for grasses to diversify leading to the proliferation of new ecosystems. The ancestors to Napier grass were one part of the grass order to diversify thanks to this.
Biology
Napier grass is your quintessential grass. With thin jointed stems that at certain times of the year branch off to produce fluffy, feather-like flowers they would not be too out of place in your average garden. However, if left to grow Napier grass can grow very tall reaching heights of 7 to 8 metres (23 to 26 feet). When they reach these giant heights you will often see the grass blades bend due to their weight, and this is not even the entire plant. Grasses, such as Napier grass, have extensive root systems which helps them draw as much water and nutrients that they can from the soil. This is also a way for them to survive being eaten, trampled on, or smothered – while the blades themselves might be damaged or die the roots will ensure that the plant lives on. This evolutionary trait has made grasses some of the most widespread and adaptable plants on the planet as they can survive situations that will overwise kill other plants.
Napier grass reproduce via two ways, again something they share with other grasses. The first is sexual reproduction. Napier grass does not rely on animals like bees or butterflies to reproduce, as many flowers do, but instead they use the wind. When their flowers bloom the wind can blow pollen from one grass to another, hopefully fertilising the plant. From there seeds develop which are scattered by either the wind or the guts of animals who eat the grass. Those that are eaten will then have the benefit of having dung as a fantastic fertiliser helping them grow. However, this method is not fool proof so the grass has another method of reproduction – asexual reproduction. As we mentioned, Napier grass has wide reaching roots and from these roots other plant shoots can push through the soil. These shoots are genetically identical to the original grass which can lead to vast areas of grassland being just one Napier grass! Often farmers will take cuttings from Napier grasses and replant them ensuring a high yield as wind pollination cannot be guaranteed to fertilise enough plants for their needs.
Distribution and Habitat
With one of their names being ‘Uganda grass’ it is not surprising that they are found in Uganda. However, Napier grass is not exclusively found in Uganda. In fact, it is found in most of subtropical and tropical Africa around the equator and the Tropics of Cancer and Capricorn. They are found from Ethiopia through the other side of Africa to Liberia and Senegal, and then south from southern Chad to Zimbabwe. Napier grass is therefore found in a range of subtropical and tropical environments, particularly grasslands and forests. Due to their usage in agriculture, more below, Napier grass has been introduced to a much wider area including South Africa, Thailand, the Philippines, Latin America, the Caribbean, the US, and Australia. In fact, Napier grass is now considered an invasive species in many of these areas.
Conservation and Threats
We are lucky that this is the first species that I’ve covered in a while that is not on the IUCN Red List of species, being classified as ‘Least Concern’ during their evaluation of the grass in 2014. A big reason for this is that Napier grass has become essential for agriculture. While we do not eat Napier grass, although it is related to millet which we do eat, this grass is used as fodder to feed the animals that humans rely on for food, milk, and materials. In their worst cases Napier grass yield 15 tonnes in one harvest making them an essential food source for cows, pigs, goats, and other farm animals. Furthermore, Napier grass is classified as a ‘pull plant’, meaning it attracts moths that would otherwise lay their eggs in desired crops making them unusable. As a result, Napier grass saves farmers a significant portion of their crop every harvest. Finally, Napier grass could be one of the plants helping us build a sustainable future. Not only does Napier grass help fight soil erosion, which threatens desertification and destitution for many farmers worldwide, but also their structure is being investigated as a potential alternative to plastics!
Bibliography:
- Heuzé V., Tran G., Giger-Reverdin S., Lebas F., ‘Elephant grass (Pennisetum purpureum)’, Feedipedia.org, (05/10/2020), [Accessed 10/05/2024]
- Rhodes, L. & Maxted, N, ‘Napier grass’, IUCN Red List, (01/07/2014), [Accessed 09/06/2024]
- Ermias Habte, Abel Teshome, Meki S. Muktar, Yilikal Assefa, Alemayehu T. Negawo, Juarez Campolina Machado, Francisco José da Silva Ledo, and Chris S. Jones, ‘Productivity and Feed Quality Performance of Napier Grass (Cenchrus purpureus) Genotypes Growing under Different Soil Moisture Levels’, Plants, 11:19, (2022)
- M. Rafiq Islam, Sergio C. Garcia, Nathu R. Sarker, Md. Ashraful Islam, and Cameron E. F. Clark, ‘Napier grass (Pennisetum purpureum Schum) management strategies for dairy and meat production in the tropics and subtropics: yield and nutritive value’, Frontiers in Plant Science, 14, (2023)
- Helen Fewster, Flora: Inside the Secret World of Plants, (London: DK, 2018)
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