PHAEOPHYTA(Brown Algae)

DICHOTOMOUS KEY OF

Prepared by:

NOE P. MENDEZCENTRAL MINDANAO UNIVERSITY (CMU)

npolomendez@gmail.com

DICHOTOMOUS KEY

Using a key teaches you about the

groups (anatomy, life style, habitat,

relations)

Versatile, adaptable

Provides consistency between users and repeat

Carry it with you – low tech

Avoid confusion between “look-a-alike”

applications = “standardization” and “quality control”Versatile

A key is a simple to use tool

Dos and Don’ts

Do proceed systematicallyDon’t jump aheadDo think about each choice

Don’t make assumptions

Do carefully note specimen characteristics

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.

Scientific classification

Domain: Eukaryota

Phylum: Phaeophyta

Class: Phaeophyceae

Kingdom:Protista

Key to Genera of the Phaeophyta1. 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. 99. 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

Ectocarpus

Sphacelaria

Colpomenia

Hydroclathrus

Sargassum

Cystoseira

Stypocaulon

Scytosiphon

Dictyopteris

Dilophus

*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

Dictyota

Lobophora

Padina

Stypopodium

Taonia

Spatoglossum

Key to the Species of

Phaeophyta

Key to species of Sargassum

1Fronds very similar to Dictyota species, but nearly wholly prostrate and with midrib; branching irregularly dichotomous

D. repens1 Fronds not similar to Dictyota (wider, taller, coarser), not prostrate;

with numerous apical cells 22

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. plagiogramma2

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

Key to the species of Dictyopteris

1Plants 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. acutiloba1

Plants medium brown to yellowish, often iridescent when fresh, blades not twisted2

2Fronds 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. ceylanica2

Fronds free of turf up to 5 cm long, shorter if in turf; characteristically nearly same width throughout, with truncate apices; branch dichotomies short

33

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. friabilis3 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

Key to the species of Dictyota

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

2Calcification very chalky and continuous on ventral "inner" surface; bright golden-yellow to orange on dorsal "outer" surface

P. melemele2

Calcification thick but discontinuous, tan on upper part of ventral surface, and throughout dorsal surface

P. japonica3 Blades distromatic throughout 4

Key to species of Padina

3Blades distromatic except at base, or blades polystromatic

54 Fronds split through nearly to base; base thick, with rust-colored rhizoids

forming a hump P. australis4

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. thivyae5

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

5 Blades three or more layers thick 66 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. boergeseni

i

Key to species of Padina

Key to species of Padina

1Fronds 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. minima1

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

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

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

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

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

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