ALGAE What aquatic biologists study as "algae" (also called pond scum, seaweeds) are actually several diverse groupings of organisms closely allied with either the bacteria (Kingdom Prokaryotae or Eubacteria, Cyanobacteria), protozoans (Crown Eukaryotes, Chromista), or primitive plants (Crown Eukaryotes, Streptophyta). What all algae have in common are photosynthetic pigments (chlorophylls) that permit these organisms, like the higher plants, to produce carbohydrates from sunlight, carbon dioxide, and water. Subtle differences in the expressed colors of the pigments associated with different groups (taxa) provide clues to an algal species' affiliation and can be used to some advantage in attempting to identify a specimen. With the exception of marine macroalgae ("seaweeds"), identification of most forms cannot proceed very far without preparing a wet mount (slide) of the specimen and examining it under a compound microscope. In the following couplets, be aware that sometimes descriptions refer to a specimen's macroscopic appearance (as seen by the naked eye), and sometimes to it's microscopic appearance (as seen through a microscope). Even specimen color can appear quite different between these two modes of viewing, and color changes also accompany preservation, including refrigeration. Determination of species in most genera is dependent upon finding reproductive structures which may not always be present. CPIE provides a list of algae known or thought to occur in Hawaiian freshwater and estuarine environments.
| 28a | (25) |
Large green alga, rather coarse, with thallus (plant body) an almost "stem-like" main axis marked by whorls of lateral filaments ~ Division CHLOROPHYTA ~ Family CHARACEAE Chara braunii
Chara zeylanica |
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| 28b | Thallus microscopic; OR if macroscopic, then structure difficult to determine without magnification, but not that of a coarse central axis with whorled side branchlets | [29] | |||
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| 29a | (28) | Under the microscope, pigmented cells are seen to be not attached to one another, or at most appear paired. Floating, or free-swimming, or settled, but usually capable of some movement | [37] | ||
| 29b | Thallus of multiple cells: either enclosed in one or more envelopes of gelatinous material, OR arranged to form simple structures such as chains, or filaments, or branching or bladelike parts; OR forming more complex, branched structures up to several cells thick | [30] | |||
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| 30a | (9) (29) |
Thallus thread-like or filamentous, { growing attached or floating and consisting of branched or unbranched very fine, thread-like structures called filaments; viewed under a microscope, filaments are single cells intimately connected end on end | [31] | ||
| 30b | Thallus is an attached or floating gelatinous mass, or an attached crust, or flattened and blade-like, or some other similar form. If thallus narrow or thread-like in some parts, then the main part more than one cell thick. | [33] | |||
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| 31a | (30) | Pigments localized in chromatophores (plastids -- internal bodies containing chlorophyll) generally evident within each cell at low power (x100) AND these plastids are a bright, grass green or yellow-green in color | [44] | ||
| 31b | Cells either without internal structures evident at low power(appearing just granular) and color not grass-green but blue-green or olive-drab, OR plastids are present and these are gray, purple, brown, red, or yellow-brown | [32] | |||
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| 32a | (31) | Cells when viewed at even relatively high power (400X) appear granular and lack internal bodies such as chloroplasts and nuclei. Color usually a gray-green, blue-green, or olive-drab, or very dark to macroscopically black | [40] | ||
| 32b | Cells with plastids (internal structures other than granules); these either gray, red, tan, or yellow-brown | [38] | |||
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| 33a | (7) (30) |
Thallus a crust or nodule, solid or hollow, soft or hard; either adherent to the substratum over a broad base or a detached mass | [35] | ||
| 33b | Thallus growing upright or lax, usually branching or a thin blade; if attached, then by a relatively narrow base (called the holdfast) | [34] | |||
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| 34a | (33) | Thallus a thin, bright green or washed-out green blade, 0.5 to 10 cm long; unbranched; if more than one blade present, then these arise from a common base. Marine to estuarine waters. Sea lettuce ~ Division CHLOROPHYTA ~ Family ULVACEAE Ulva fasciata
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| 34b | Thallus stiff or lax, highly branched, and without blade-like parts. Color some shade of red, or yellowish-brown to greenish-brown | [54] | |||
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| 35a | (33) | Mass or crust soft, firm, or hard, but comprised of a gelatinous martrix embedded in which are algal cells arranged in chains, filaments, or packets. Cells viewed at relatively high power (400X) appear granular and lack internal bodies such as chloroplasts and nuclei. {Color gray-green, blue-green, or olive-drab, often very dark (appearing black), or some shade of red | [40] | ||
| 35b | Mass or crust soft or hard, but comprised mostly of cells, rather than extracellular matrix | [36] | |||
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| 36a | (35) (54) |
Alga a thin crust of very small, reddish cells comprised of short, densely packed filaments (a pseudoparenchyma); { maroon encrustations on smooth basalt in fast flowing streams, frequently in shaded situations ~ Division RHODOPHYTA ~ Family HILDENBRANDIACEAE Hildenbrandia sp.
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| 36b |
Alga a closely adherent mass of bright green cells ~ Division CHLOROPHYTA ~ indet. sp.
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| 37a | (29) | Cells with one or more flagella (whip-like structures used for movement); motile, movement fairly rapid with slight swinging motion of cell evident even if flagellum too delicate to see | [Note D] | ||
| 37b | Cells lacking flagella; if moving, then by a slow, 'gliding' process. Cell wall an ornamented, siliceous (glass) case. Chromatophores some shade of brown (usually yellow-brown). Diatoms ~ Division BACILLARIOPHYTA |
[65] | |||
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| 38a | (32) | Filament unbranched, consisting of cells with glass-like and ornamented cell walls. Chloroplasts yellowish to brownish in color. Diatoms ~ Division BACILLARIOPHYTA |
[66] | ||
| 38b | Filament branched or (rarely) unbranched, consisting of unornamented cells with flexible cell walls | [39] | |||
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| 39a | (36) | Chloroplasts yellow brown or yellow-green. { Thallus sparsely branched or unbranched | [43] | ||
| 39b | Chloroplasts a shade of bluish-gray or red or orange. { Thallus usually profusely branched ~ Division RHODOPHYTA |
[55] |
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Note D:
- Your identification is leading to a group of microscopic organisms which, because of very small size and difficult taxonomy, is not treated further in this key.