KEYS TO COMMON GENERA AND SPECIES

DISCLAIMER: These keys and species identities are provided for informational purposes only. We can take no responsibility for any consequences of misinterpreted information presented here. Always consult your local algae specialist if you have questions.

The 16 genera listed in this key represent about 50% of the green algal genera in the Hawaiian Islands. Some of the lines in this key end in a specific name which indicates that there is only one species in the genus. The number in parentheses that follows a genus name is the number of species recognized for that genus at this time in Hawai’i. Isabella Abbott, January 1997.

1	Plants filamentous (=single or multiple rows of cells, branched or unbranched)	2
1	Plants blade-like, tube-like, and other shapes or forms; in general not filamentous	4
2	Filaments unbranched	3
2	Filaments slightly to profusely branched; plants usually in soft to stiff clumps, often floating; attachments by rhizoids frequently from basal poles of mid to lower cells, or by cluster of basal rhizoids	Cladophora (6 spp)
3	Plants usually in erect tufts; filaments consisting of large cells between 100-600 µm in diam., nearly isodiametric; single basal cells modified for attachment	*Chaetomorpha* (3 spp)
3	Plants not tufted, mostly unattached or lying loosely on mud or rocks; filaments with cells 2-4 times longer than wide; rhizoidal branchlets lacking, basal only, or along length of filament	*Rhizoclonium* (3 spp)
4	Plant bodies arranged in blades or tubes	5
4	Plant bodies in other shapes or forms	7
5	Blades one or two-cells thick (a thin section should be cut with a razor blade and examined under magnification)	6
5	Blades (when sectioned, as above) tubular at least near the base	Enteromorpha (6 spp)
6	Blades one-cell thick, cells in surface view sometimes aggregated into packets	*Monostroma* (2 spp)
6	Blades two cells thick; cells in surface view not aggregated	*Ulva* (4 spp)
7	Some portion of the plant netlike	8
7	Plants not netlike	10
8	Bulk of plants that are up to 6 cm tall clearly netlike throughout	9
8	Plants not more than 3 cm tall, only distal part netlike; remainder of plant with relatively conspicuous uniseriate stem-like portion	*Struvea anastomosans*
9	Plants very dark emerald green, surface soft and spongy, rarely with epiphytes	*Boodlea composita*
9	Plants usually medium green or bleached yellowish, surface firm, sometimes shiny; meshes of net often occluded by epiphytes	*Microdictyon* (2 spp)
10	Plants not calcified	11
10	Plants lightly to heavily calcified	22
11	Erect axes connected to creeping (prostrate) axes	12
11	Erect axes without creeping connecting axes	15
12	Reproductive structures cut off from bearing branches	13
12	Reproductive structures produced from ordinary branches	14
13	Reproductive structures localized in whorled branches	*Caulerpella ambigua*
13	Reproductive structures formed in gametangia	*Trichosolen oahuensis*
14	14 - Erect axes branched radially or verticillately, or appearing to be continuation of axes; terminal branches spongy, grape-like, fan-like, feather-like, zig-zag, and other shapes	*Caulerpa* (7 spp)
14	Erect axes branched pinnately or to one side (secund), not further branched or elaborated	*Bryopsis* (2 spp)
15	Plants unbranched, resembling small, single glass balls up to 4 cm in diam., usually under turf or in limestone	*Ventricaria ventricosa*
15	Plants branched, with large, transparent cells less than 1 cm in diam	16
16	Cells visible without magnification, laterally cohering or arranged in irregular clumps	17
16	Cells not visible without magnification, arranged in intertwined tightly woven filaments showing large diameters when teased apart	18
17	Branching divisions irregular	19
17	Branching divisions regular at first in single layer, cohering cells forming a solid or hollow cushion (sometimes open)	*Dictyosphaeria* (2 spp)
18	Plants often resembling asymmetric, torn paddles; surfaces woolly or felt-like, dark olive brown, never producing pinkish liquid on standing in fresh water	Avrainvillea amadelpha
18	Plants not paddle-like, but with many different forms; surfaces velvety, sometimes bead- like; usually dark green, always producing pinkish liquid when standing in fresh water	Codium (12 spp)
19	Branches not constricted except where attached	20
19	Branches constricted throughout	*Chlorodesmis caespitosa*
20	Plants forming extensive erect, crisp clumps; branches and axes shaped like irregular bottles	*Valonia* (2 spp)
20	Plants forming tufts or mats, the branches not like bottles	21
21	Plants forming erect almost crystalline tufts; branches formed by protrusions of rounded-up protoplasts from previous order; final branches radially arranged	*Siphonocladus tropicus*
21	Plants forming irregular mats, usually decumbent; branches divided irregularly dichotomously, their terminal ends often producing secondary attachments to substratum	*Cladophoropsis* (3 spp)
22	Plants with disc-like jointed flattened calcified segments, mostly white, with photosynthetic portion often restricted to tops of plants	*Halimeda* (7 spp)
22	Plants without disc-like segments	23
23	Small umbrella-like plants no more than 5 mm tall, attached by siphonous stipe	*Acetabularia* (3 spp)
23	Plants fan-like, small balls, or worm-like	24
24	Calcification restricted to walls of fan-shaped filaments and upper portion of stipe	*Rhipidosiphon javensis*
24	Calcification restricted to ends of lateral branches, forming a cortical layer	25
25	Plants mostly white, worm-like with tufts of hairs at apices; calcification obvious except at apices	*Neomeris* (2 spp)
25	Plants mostly green, surface hexagons representing ends of lateral branches that are coherent	*Bornetella sphaerica*