Classification of Azolla




Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae.The genus Azolla was established by the French naturalist Jean-Bapitiste Lamarck in 1783 based on the specimens collected by Philibert Commerson and his assistant Jeanne Baré from the Magellan region of South America during Louis-Antoine de Bourgainville’s1766-1769 expedition around the world:


“It is a small aquatic plant which appears to float on the water surface in the manner of Lenticules (Lemna) with whom it seems to have a great relation and which nevertheless looks like a small fern.” (translation from the French)
Lamarck’s observation of Azolla’s habitat must have been based on Commerson’s own observations because at this time Azolla was not native to Europe.
Lamarck did not refer to the origin of the name that he gave Azolla, only saying that:
“Cette plane a ete rappertee de Magellan par M. dr Commerson”. (This plant was brought from Magellan by Mr. Commerson).
Traditionally, the name is referred to a conjugation of two Greek words, azo (to dry) and allyo (to kill), because the fern is killed by drought, but Carrapiço (2010) has suggested that the name was adopted from a word used by the local population in Argentina or Chile where Commerson collected his specimens of Azolla.
Perhaps both versions are true. Maybe Lamarck was aware of the local usage and then constructed a name that sounded similar using a Greek nomenclatural base.


The genus Azolla was established by the French naturalist Jean-Bapitiste Lamarck in 1783 based on the specimens collected by Philibert Commerson and his assistant Jeanne Baré from the Magellan region of South America during Louis-Antoine de Bourgainville’s1766-1769 expedition around the world:

“It is a small aquatic plant which appears to float on the water surface in the manner of Lenticules (Lemna) with whom it seems to have a great relation and which nevertheless looks like a small fern.” (translation from the French)

Lamarck’s observation of Azolla’s habitat must have been based on Commerson’s own observations because at this time Azolla was not native to Europe.

Lamarck did not refer to the origin of the name that he gave Azolla, only saying that:

“Cette plane a ete rappertee de Magellan par M. dr Commerson”. (This plant was brought from Magellan by Mr. Commerson).

Traditionally, the name is referred to a conjugation of two Greek words, azo (to dry) and allyo (to kill), because the fern is killed by drought, but Carrapiço (2010) has suggested that the name was adopted from a word used by the local population in Argentina or Chile where Commerson collected his specimens of Azolla.

Perhaps both versions are true. Maybe Lamarck was aware of the local usage and then constructed a name that sounded similar using a Greek nomenclatural base.
Definition of the genus Azolla

The genus Azolla is defined as a heterosporous leptosporangiate fern from aquatic and semi-aquatic habitats. It is assigned to the monogeneric Family Azollaceae.



Subdivision of the genus

Azolla’s speciation has varied according to various authors’ interpretations and it is presently undergoing revision. According to Francisco Carrapiço (personal communication to J. Bujak), the genus Azolla has six species and three subspecies:

“The problem related to the modern Azolla species is still an open question, but based on the classification proposed by Saunders & Fowler (1993) we can consider the following species and subspecies:

Species:

Azolla caroliniana

Azolla filiculoides

Azolla mexicana

Azolla microphylla

Azolla pinnata

Azolla rubra

Subspecies:

Azolla pinnata subsp. africana

Azolla pinnata subsp. asiatica

Azolla pinnata subsp. pinnata

Azolla also has several fossil species which date back approximately 70 million years to the Late Cretaceous.  These include Azolla arctica which were deposited 50 million years ago during the Eocene Arctic Azolla Event.



Azolla hybrids

Hybrids are commonly produced and selected because they have desirable characteristics not found or inconsistently present in the parent individuals or populations. Hybridization is the result of interbreeding between two animals or plants of different taxa, including species, genera and, in rare cases, families.

Hybrids between different species of the same genus are known as interspecific hybrids or crosses. Hybrids between different sub-species are known as intra-specific hybrids. Hybrids that result from crosses between populations are known as breeds or cultivars of a single species.

Azolla hybrids have been developed to improve the plant’s temperature tolerance and biomass production.  For example, hybridization between A. microphylla and A. filiculoides improves annual biomass production, as illustrated by a study by Van Cat et al. (1989).

In the parent material, the latter grows better in the spring, while the former grows better in the summer and autumn due to its higher-temperature tolerance. The hybrid, however, produced biomass comparable to that of A. filiculoides in the spring and comparable to that of A. microphylla in the summer and autumn, thus boosting overall annual production. Van Cat et al. (1989) showed that the hybrid did not show stress (characterized by a red color) under phosphorus- or calcium-deficient conditions and that the hybrid had a higher nitrogen content than the parent A. microphylla. Biomass production in the field was also higher in the hybrid than that of A. microphylla.

In another study, Kannaiyan & Kumar (2005) screened Azolla hybrids AH-Cl, AH-C2, AH-C3 and AH-C4 with wild cultures of A. filiculoides and A. microphylla to produce a better biomass. They found that Azolla hybrids produced a greater biomass than wild cultures of A. filiculoides and A. microphylla.  AH-C2 produced the greatest biomass with a shorter doubling time and a higher relative growth rate followed by AH-C1.