7.2: Lycophytes

There are approximately 1,300 species of lycophytes worldwide (Christenhusz and Byng, 2016) and they can be found in arctic, temperate, and tropical regions. In Hawai‘i, there are 17 native species and varieties and at least 4 introduced species that have become naturalized (Ranker et al., 2019).

Lycophytes first appeared in the Silurian period approximately 425 million years ago (Appendix 1). By the Carboniferous period (350 million years ago), they had become the dominant plant group and formed extensive dense forests. The species living at that time and that are now extinct, ranged from short plants to massive trees up to 30 meters (98 feet) in height (Figure \(\PageIndex{1}\)). These plants were very common in swamp forests and their biomass was responsible for the formation of coal deposits, from which we extract coal today. In the late Carboniferous, the climate on Earth changed, drying the swamps and pushing most lycophytes to extinction. Today the living species of lycophytes are all relatively few and small compared to their once lush diversity.

Figure \(\PageIndex{1}\): Artistic reconstruction of Lycophytes from the Carboniferous period. Lepidodendron sternbergii and Lepidondendron elegans by Biblioteca Rector Machado y Nuñez, Public Domain.

Lycophytes are divided into three groups (orders): Lycopodiales, Seleginellales and Isoetales:

Lycopodiales (club mosses, fir mosses)

There are four groups of Lycopodiales in Hawai‘i (Huperzia, Lycopodium, Palhinhaea, Phlegmariurus, per PPG I, 2016). Some species may resemble small pine trees with “cones” growing on the tip of their branches. These cones are spore-bearing structures called strobili (singular, strobilus). They are made up of tiny, closely spaced leaves with sporangia (spore cases) hiding at their bases. Species in this group are usually smaller than 30 centimeters (1 foot) but can reach more than a meter (5 feet) tall in some tropical ecosystems. Hawai‘i has fifteen species and a few hybrids (Ranker et al., 2019), which are commonly found in wet forests (Figure \(\PageIndex{2}\)).

Figure \(\PageIndex{2}\): Wāwaeʻiole (Phlegmariurus phyllanthus), is a species in the Lycopodiales native to the Hawaiian Islands. By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr. A derivative of the original work by Forest and Kim Star licensed under CC BY 3.0 via Wikicommons. Modified to include labels.

Selaginellales (spike mosses)

Spike mosses have stems with many branches and scale-like leaves that grow in a spiral-like pattern, each having a little tongue-like extension called a ligule (Figure \(\PageIndex{3}\)). Spike mosses can be found in wet environments, growing alongside mosses and liverworts. In Hawai‘i, there are 2 native species (one endemic and one indigenous) and four introduced species that became naturalized (Ranker et al., 2016).

Figure \(\PageIndex{3}\): Selaginella arbuscula (Lepelepe a moa) is a spikemoss native to Hawaiʻi. By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr.

Isoetales (quillworts)

Quillworts are aquatic plants with long narrow leaves that are wider at the base and are arranged in a spiral (Figure \(\PageIndex{4}\)B). Hawai‘i only has one species of quillwort, Isoëtes hawaiiensis, which is endemic (Taylor et al., 1993). This species is quite rare and has only been found on Maui and Hawai‘i Island. On Maui, it occurs in the West Maui Mountains (Mauna Kahālāwai) on top of Pu‘u ‘Eke elevation 1372 meters (4,500 ft; Figure \(\PageIndex{4}\)A).

Figure \(\PageIndex{4}\): A) Pu‘u Eke on the Island of Maui, where populations of Isoëtes hawaiiensis are found (Photo Credit: Royce Bair). B) Isoëtes hawaiiensis, a quillwort species endemic to the Hawaiian Islands (Photo Credit: Earth.com). By DutraElliott is licensed under CC BY-NC-SA 4.0 via Flickr.