**3. Systematics and taxonomy of macroalgae**

It was the French botanist Joseph Pitton de Tournefort (1656–1708) who grouped the species into genera and then the Swedish naturalist Carl von Linné (1707–1778), founder of systematics (or taxonomy), who classified the organisms into increasingly large groups: species, genera, families, orders, classes, phylum (or phyla), and kingdoms. Algae, according to Feldmann and Chadefaud [20, 21], are classified into six branches differentiated by the nature of the pigments, the nature and situation of carbohydrate reserves, and the presence or absence, number, and arrangement of flagella:


**5**

*Algae Essential Oils: Chemistry, Ecology, and Biological Activities*

• Phaeophycophyta: brown algae; always multicellular and almost exclusively

• Rhodophycophyta: red algae; mainly multicellular and mostly marine

There are about 2000 species (in 265 genera) of brown algae [22], and less than 1% are known from freshwaters (3–7 genera) [23]. The brown color is due to Fucoxanthin (carotenoid pigment) and in some species to the presence of tannins

There are estimated to be at least 600 genera with 10,000 species within the green algae [24] recognized inhabiting mostly in the water's surface of the calmer seas. They are characterized by the presence of chloroplasts with two envelope membranes, stacked thylakoids, and chlorophyll a and b. In their fundamental biochemistry (photosynthetic pigments, storage polysaccharides, etc.), the

They are primarily marine in distribution sometimes inhabiting the deep water, with less than 3% (150 species from 20 genera) of the over 6500–10,000 species occurring in truly freshwater habitats [25]. The red algae are characterized by eukaryotic cells, with the complete absence of flagellar structures, food reserves of starch, presence of phycobilins, chloroplasts without stacked thylakoids, and no

The fragrances of terrestrial plants have aroused human interest since antiquity; they were related to spiritual and civilizational aspects. It is not surprising that the first research work on odorous volatile products was carried out on aromatic plants. Phytochemists have quickly associated the odors emanating from trees and shrubs to terpenes (notably monoterpenes), spices to phenols and derivatives, and fruits and flowers to aldehydes, esters, and ketones. The smell connected with marine flora are much less familiar. Unlike the wide number of terrestrial odoriferous plants, relatively few marine seaweeds possess an attractive odor. Although the natural products chemistry of terrestrial organisms was known before the nineteenth century, the one of the marine derived is more recent, and it has only emerged over the past 75 years. This is due to the complexity to access the marine environment. The marine natural products had become an important subdiscipline of natural products chemistry, which has experienced a particular craze which has led to the isolation and characterization of thousands of secondary metabolites belonging to original chemical skeletons without equivalent in the terrestrial environment. Historically, volatile oils of terrestrial plants were used in Chinese [26] and Egyptian civilizations [27–29] few centuries ago, whereas the first works on the isolation of volatile products of marine algae were carried out, on the brown alga *Fucus* [30] and the red algae *P. fastigiata* and *P. nigrescens* [31] when the seaweeds are exposed to air, at the beginning of the 1930s, followed later by the Katayama

*DOI: http://dx.doi.org/10.5772/intechopen.91672*

**3.1** *Phaeophyceae* **(or Fucophyceae)**

Chlorophyta resemble the higher plants [24].

**4. Chemistry of marine algae volatile compounds**

external endoplasmic reticulum.

marine

(phenolic compounds).

**3.2** *Chlorophyta*

**3.3** *Rhodophyta*

