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 Ám 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

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