3. Using a key teaches
you about the groups
(anatomy, life style,
habitat, relations)
Versatile,
adaptable
4. Dos and
Don’ts Do proceed
systematically
Don’t jump
ahead
Do think
about each
choice
Don’t make
assumptions
Do carefully
note specimen
characteristics
5. The Phaeophyta are almost entirely marine,
frequently dominating rocky shores in cold and
temperate waters throughout the world.
The colors of brown algae (predominantly due to the
brown accessory pigment fucoxanthin) cover a spectrum
from pale beige to yellow-brown to almost black. In
tropical seas, they range in size from microscopic
filaments to several meters in length.
7. Key to Genera of the Phaeophyta
1. Tinted algae, less than 1 mm wide, whose shape can only be discerned
using a microscope. They often cover surfaces. 2
*1. Algae larger than the above, distinguished by the shape of their thallus
without magnifying equipment. 3
2. The thallus is made of a single row of cells. The spore-ridden sporangium
are found at the edge of the thallus. Ectocarpus
*2. With the aid of a microscope, one may see several rows of cells along the
width of the thallus. The triangular or star-shaped sporangium has three or
four horns. Sphacelaria
3. Hollow, globular algae, mostly irregular. 4
*3. Flattened or branched algae. Algae otherwise. 5
4. Numerous holes (spaces) in the algal thallus resemble a net or fishing net.
The holes are irregular in size . Hydroclathrus
*4. The algal thallus is continuous (no holes) and often covered with a
smooth mucous layer. The algae’s interior contains gasses. Colpomenia
5. Algae are rigid, resembling higher plants. Relatively large algae, reaching
up to 20 cm and more. 6
*5. Algae otherwise. 7
6. The thallus resembles a ‘stalk’ and ‘leaves’. The reproductive
organs are located on separate branches. Round flotation blades
are held by prickles along the ‘stem’. Sargassum
*6. The ‘stem‘ is mostly flat, often winged, sometimes
cylindrical. Elongated floatation cysts that form a part of the stalk
are sometimes missing. Cystoseira
7(5). Flattened algae, that if hollow, are much longer than they
are wide. 8
*7. Algae incorporating a central axis with numerous side
branches. The arms generally resemble a feather. Each side
branch is smaller than 1 mm. Stypocaulon
8. Cylindrical, hollow and unbranched algae, 1-5 mm wide and up
to 20 mm length. They grow in the upper regions of the intertidal
zone and are sometimes exposed to air. Scytosiphon
*8. Algae that aren’t hollow. Algae otherwise. 9
9. The algae body resembles a central axis with membranous
wings on either side. Dictyopteris
*9. Membranously wingless algae. Algae otherwise. 10
10. Flat algae with regular, dichotomous branching. Growth is
generated from a single apical cell or two (microscope
required). 11
*10. Fan-like algae, strand-like algae, algae otherwise. 12
11. The upper part of the thallus is rounded and often widens
(spatula-like). Through a microscope, three layers of cells can be
discerned. Dilophus
13. *11. The edges of the branches do not widen or round off. A two-layered medulla
of cells can be discerned through a microscope. Dictyota
12. Fan-like algae where, sometimes, especially in mature individuals, the fan splits
into several lobes. 13
*12. Algae otherwise. 15
13. Concentric lines appear along the thallus’ breadth. 14
*13. The thallus resembles flattened lobes, loosely attached to rocks. The algae is
coloured shades of brown–yellow and characteristically grows in shady areas of the
subtidal zone. Lobophora
14. Extremely common algae. The thallus contains calcium, and its edges curl
backwards. Padina
*14. The alga does not calcify. Plants immersed in water have a phosphorous
shade of azure. Growth generates from a row of apical cells (a
microscope is required. Stypopodium
15(2). Soft, strand-like algae, unbranched and narrow at the bottom. Plants are
commonly found in the upper region of the intertidal zone. Petalonia
*15. The thallus splits into irregular, lineal strands. 16
16. Fan-like algae that split into (usually) dichotomous strands. The further
they are from the algal base, the narrower the strands become. The algae is bright
brown and seems to have dark lines along its breadth . Taonia
*16. The algal surface is rough. It is dark-brown, but when exposed to air,
the thallus changes colour to dark green. Branching is dichotomous. Spatoglossum
19. 1
Fronds very similar to Dictyota species, but nearly wholly prostrate
and with midrib; branching irregularly dichotomous
D. repens
1 Fronds not similar to Dictyota (wider, taller, coarser), not prostrate;
with numerous apical cells 2
2
With veinlets visible to naked eye, forming acute angles to the midrib;
sporangia or gametangia in linear patches parallel to midrib; blade
mostly distromatic from margin to midrib
D. plagiogramma
2
Veinlets microscopic and faint; sporangia or gametangia in rows
starting at midrib and arching downward to lateral margins; blade
monostromatic for up to 15 cells from margin, then di-polystromatic to
midrib
D. australis
Key to the species of Dictyopteris
21. 1
Plants dark chocolate brown, fronds tightly to loosely spiralled (twisted) axes up to 3 mm in
diam., terminal dichotomous division about 1 mm in diam
D. acutiloba
1
Plants medium brown to yellowish, often iridescent when fresh, blades not twisted
2
2
Fronds rarely more than 4 cm long, less than 2 mm at widest, then narrowing abruptly toward
apices; on same plant, some portions may be 2 to 3 mm wider than other places
D. ceylanica
2
Fronds free of turf up to 5 cm long, shorter if in turf; characteristically nearly same width
throughout, with truncate apices; branch dichotomies short
3
3
Fronds golden with bluish iridescence until removed from water, often in turf on sides of tide
pools; in surface view some superficial cells having L-shaped lenticular thickenings
D. friabilis
3 Fronds yellowish-green, iridescent, occasionally whole plant with 1-2 twirls, but fronds not
twisted; no lenticular thickenings; lateral margins with many proliferations of various lengths
and sizes D. sandwicensis
Key to the species of Dictyota
23. 1 Fronds heavily calcified on ventral "inner" surface, nearly obscuring
hair and sporangial lines 2
1 Fronds lightly calcified, mostly as a very thin sheet of gray, hair and
sporangial lines clearly observable 3
2
Calcification very chalky and continuous on ventral "inner" surface;
bright golden-yellow to orange on dorsal "outer" surface
P. melemele
2
Calcification thick but discontinuous, tan on upper part of ventral
surface, and throughout dorsal surface
P. japonica
3 Blades distromatic throughout 4
Key to species of Padina
24. 3
Blades distromatic except at base, or blades polystromatic
5
4 Fronds split through nearly to base; base thick, with rust-colored rhizoids
forming a hump P. australis
4
Plants not split, but blades laterally adhering to each other, frequently to
the base and difficult to separate without tearing; almost always in large
clumps
P. thivyae
5
Blades distromatic in upper parts, tristromatic below; sporangia grouped
above every hair line on inner surface, hairs lacking on opposite surface
P. tenuis
Key to species of Padina
25. 5 Blades three or more layers thick 6
6 Blades 4 cells thick in upper frond, up to 9 cells thick below;
sporangia grouped above every hair line on inner surface, hairs
lacking on opposite side P. Crassa
6 Blades mostly 3-celled (rarely 2-celled) throughout, sporangia
grouped above every hair line on inner surface, but both groups
alternating with a hair line on opposite surface
P. boerges
enii
Key to species of Padina
27. 1
Fronds erect from a discrete base, silky colorless hairs
common along mid an upper parts of plants; growing high
in the intertidal region, usually on vertical or sloping
igneous rocks
C. minima
1
Fronds decumbent to prostrate, bases spreading; axes
terete, without colorless hairs; usually growing on
horizontal calcareous surfaces below low tide on reef flats
C. implexa
Key to the species of Chnoospora
28. 1 Fronds soft, erect but lax; branching dichotomous,
axes less than 2 mm in diameter, apices hair-like R. orientalis
1 Fronds forming matted cushions composed of many
tightly adhering branches, irregularly dichotomously
divided R. intricata
Key to the species of Rosenvingea
29. Key to species of Sphacelaria
1 Arms of modified lateral branches
(propagula) cylindrical, like a broad V S. rigidula
1 Arms of propagula not cylindrical,
approximately triangular or club-like in
outline 2
2 Propagula club-like, top rounded or
thickened S. novaehollandiae
2 Propagula triangular, like a top; plant tufts
dense and nearly black S. tribuloides
30. 1 Plants with extensive matted rhizoidal systems
endophytic among utricles of Codium species;
spindle -shaped plurilocular structures near basal
portion of plants F. elachistaeformis
1 Plants with a small number of rhizoids;
endo/epiphytic on a wide variety of hosts; plurilocular
structures cylindrical, distributed throughout plants
below meristematic regions F. indica
Key to species of Feldmannia
31. 1 Intertidal, in rope-like strands, cells of filaments
isodiametric to twice as long as broad, hook-like or
short lateral branches present; plurilocular organs
about as long as broad
H.
breviarticulata
1 Subtidal, not rope-like, cells becoming larger than twice
their diameter, without hooklike lateral branches;
plurilocular organs cylindrical more than twice as long
as broad attached alternately or adaxially H. mitchelliae
Key to species of Hincksia
