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About Seaweeds
Figure 8. The three-phased life cycle of the red seaweed Gracilariopsis. Separate haploid gametophytes, male (A) and female (D), produce non-motile sperm (B, C) and attached eggs (E). The sperm encounters a bowling pin–shaped egg and fuses with it (E). The resulting zygote develops into a parasitic diploid phase on the female gametophyte (F, G). This parasitic phase produces spores (H, I), which are released and develop into a free-living diploid phase (J). The free-living phase then produces spores (K, L) by meiosis (reduction cell division). These spores develop into male and female gametophytes—the sexual phase.
A
B
C
G
D
E
F
H
I
J
K
L
syngamy
meiosis
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Seaweed Names
Every known species has a scientific name, and some species also have a common name. For example, Nereocystis luetkeana is the scientific name for the species commonly known as “bull kelp.” The common name is the name by which a species becomes known among lay people and can be very useful, especially in cases where the common names are universally applied, such as with breeds of dogs and species of birds. However, in most cases a common name may refer to any of several species and is often haphazardly applied or region specific. For example, ask someone from the Pacific Northwest to show you “bull kelp” and they point to Nereocystis luetkeana; ask the same of someone from Australia, New Zealand or South Africa and they point to Durvillaea antarctica, a different species altogether. On top of that, a single species may have more than one common name: Nereocystis luetkeana is also (though much less frequently) known as “bladder kelp” or the delightfully imaginative “sea otter’s cabbage.”
In contrast, the critically important feature of scientific names is their lack of ambiguity: Nereocystis luetkeana applies to only one species, allowing confident communication about this species by scientists and professionals no matter where they are in the world—this is the power and beauty of scientific names.
The two parts to the name are informative. The first part is the “generic” or “genus” name and is applied to multiple species when they are closely related—e.g., the lion (Panthera leo) and tiger (Panthera tigris).The second part (e.g., leo) is the “specific” or “species” name and tells you that you’re talking about a lion and not a tiger. Both a genus and a species are required in a scientific name. These names are usually derived from Latin or Greek—which can make them tongue-twisters—and may or may not describe some feature of the species: e.g., the name of the five-rib kelp, Costaria, comes from the Latin costa (a rib), but the sea palm kelp, Postelsia, is named for the Estonian naturalist Postels.
The majority of our seaweeds do not have widely accepted common names. In this guide we include only those common names that we consider to be well established. Our advice is to use the scientific name and attach a descriptive phrase if you find this helpful; for example: Costaria costata, the five-ribbed kelp.
Species of seaweed are classified in a taxonomic hierarchy that reflects their relatedness. This hierarchy is universally applied to all living things and
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About Seaweeds
some that are not (fossils). For example, Saccharina latissima (sugar kelp), a brown seaweed, is classified as follows:
Kingdom: Chromista. A kingdom is a large grouping of vaguely similar species thought to share a distant common ancestor. Other kingdoms include Animalia and Plantae.
Division: Phaeophyta (brown algae). A division is a slightly smaller group of species thought to share a common ancestor. The animal equivalent to division is phylum. The -phyta suffix designates divisional status. Other divisions include Chlorophyta (green algae) and Rhodophyta (red algae).
Class: Phaeophyceae. Classes designate groups within a division that have significant differences but are closely related. For example, birds and mammals form separate classes within the phylum Chordata (animals with backbones). The -phyceae suffix designates class. Other classes include Chlorophyceae (most green algae) and Bacillariophyceae (the diatoms).
Order: Laminariales. A class is subdivided into orders on the basis of features such as body plan and life cycle. In the brown seaweeds, the order Laminariales (large brown algae, the kelp) have intercalary growth, the Ectocarpales (small filamentous brown algae) have diffuse growth and the Fucales (common brown rockweeds) have apical growth. The -ales suffix designates ordinal status.
Family: Laminariaceae. Orders are subdivided into families on the basis of various features. Earlier, most members of the laminarialean family Alariaceae (the winged kelp) had sporophylls (special blades for spore production) and no branching. Most members of the laminarialean family Lessoniaceae were regularly branched and did not have sporophylls. The Laminariaceae lacked sporophylls and branching. Today, we know those features don’t reflect true relationships and the families of kelp are now defined by molecular DNA differences. The -aceae suffix designates familial status.
Genus: Saccharina. We can define a genus (plural: genera) as a group of closely related species that are usually not interfertile and are distinguished on the basis of some relatively small morphological feature, such as branching pattern. There may be several genera in a family. The generic name is always italicized or underlined.
Species: Saccharina latissima (Linnaeus) C.E. Lane, C. Mayes, L. Druehl and G.W. Saunders. Individuals making up a species are thought to be sexually compatible. Different species within a genus are considered to be sexually
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incompatible or at least sexually isolated. In reality, this sexual criterion is rarely confirmed. Most species recognized today were established on the basis of morphological features prior to our understanding of the significance of interbreeding and sexual isolation. A new twist in defining and distinguishing between species (and higher taxonomic groups) is the application of DNA sequences (e.g., see Biodiversity, the DNA Barcode and the Future of Taxonomy, below). The species name is italicized or underlined. Following the species name are other names (not italicized), which give more