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ОглавлениеChapter 2. Identification Keys for the Aquatic Plants of Pennsylvania
The keys in this book are designed to guide the user through a series of decisions leading to proper identification. At each step of the key, the user must examine a characteristic or characteristics of the plant and decide which of a pair of corresponding statements best fits the specimen in question. Each statement and its corresponding member are preceded by the same capital letter(s). There are a few simple rules that, if followed carefully, should ease the task of arriving at a correct identification.
1. Read each statement of a pair carefully and thoroughly before deciding which best fits the plant you are looking at.
2. Be sure you understand any botanical terminology used in the statements before moving on to the next step. Consult the glossary at the back of the book if you are not certain.
3. Look at more than one example of the characteristic in question. For example, if the key asks about the number of petals present in a flower, look at more than one flower.
4. Don’t dwell on the exceptions! Most plant species are quite variable. Throughout the keys you will see qualifiers such as “often,” “usually,” or “mostly” to account for the lack of uniformity.
5. After reaching a tentative identification, read the descriptions and look at the illustrations to confirm that you are correct.
6. Make your observations slowly and carefully, especially if you are new to “keying out” plants.
For convenience the initial key below divides aquatic plants into six groups based on growth habit: emergent, floating-leaf, submergent, etc. The next step is to use the section keys to arrive at a genus and finally the keys to each genus, which are found in the succeeding chapters, to name a plant to species.
The keys assume the plant’s appearance under normal water levels. Many species assume unusual growth habits and/or morphological forms when the water is unusually deep or shallow. Some species will appear in more than one habit category, since they assume more than one form under normal conditions. Whether a plant is considered emergent, submergent, or floating depends on whether the main body (leaves and/or primary axis) occurs above, below, or at the surface of the water. Species that produce only their flowers above the water surface are not considered emergent or floating-leaved. Be aware that exceptional variations may, and occasionally do, occur.
Key to Growth Habit Groups
A. plants without distinguishable leaves and stems, or tiny floating plants with minute leafy stems (leaves less than 1 mm long) ........................................................................... Thalloid and/or tiny floating plants, p. 163
A. plants with distinct leaves and/or stems; leaves, if present, more than 1 mm long
B. plants with at least some leaves and/or stems held above the water surface ........................................................................... Emergent plants, p. 29
B. plants entirely under water or with at least some leaves floating at the surface
C. plants with at least some leaves floating on the water surface ............................................................. Floating-leaf plants, p. 143; or some pondweeds (Potamogeton spp.), p. 186
C. plants with leaves entirely or mostly under water, or buried in a sandy or peaty substrate; at most flowering above the surface or with only leaf tips floating at the surface; or stems sometimes leafless
D. underwater leaves broad to very narrow, but not finely divided
E. underwater leaves attached to an elongate stem, or submergent stems sometimes leafless, plants rooted or free-floating ............................................................. Submergent leafy-stemmed plants, p. 183
E. underwater leaves in a basal rosette, plant rooted on the bottom ................................................ Submergent rosette-forming plants, p. 241
D. underwater leaves very finely divided ............................................................................. Submergent plants with finely divided leaves, p. 255
Figure 2.1. Stems jointed, tiny scalelike leaves in whorls at the node (×3/4).
Key to Emergent Plants
A. emergent leaves long and narrow, their blades more than 7 times longer than broad, or leaves absent
B. leaves absent
C. stems jointed; tiny, scale-like leaves in whorls at the nodes ................................................................... water horsetail (Equisetum spp.), p. 88
C. stems not jointed, not branching in whorls
D. inflorescence appearing lateral ....... bulrush (Schoenoplectus spp.), p. 47
D. inflorescence terminal ................. spike-rush (Eleocharis spp.), p. 111
B. leaves present
E. leaves all basal
F. leaves expanded at the base and containing spore sacs ...................................................................... quillwort (Isoetes spp.), p. 245
F. leaves not expanded at the base, lacking spore sacs
G. leaves mostly not more than 10 cm long ................................................................... pipewort (Eriocaulon spp.), p. 243
G. leaves mostly more than 50 cm long ................................................................ flowering-rush (Butomus umbellatus), p. 76
E. at least some leaves cauline
H. perianth ............................................. showy iris (Iris spp.), p. 90
H. perianth not showy, reduced to a few bristles, or absent
I. individual flowers of the inflorescence subtended by 1 or 2 bracts
J. stems mostly triangular at the base; each flower subtended by 1 bract
K. flowers in spikelets with 2-ranked scales ......................................................... three-way sedge (Dulichium arundinaceum), p. 121
Figure 2.2. Leaf expanded at the base, containing spore sac (×3/8).
K. flowers in spikelets with spirally arranged scales
L. spikelets with 1 perfect flower and 1 achene ............................................. twig-rush (Cladium mariscoides), p. 123
L. spikelets with many perfect flowers and many achenes .................................. bulrush (Scirpus ancistrochaetus and Schoenoplectus spp.), p. 47
J. stems round at base; each flower subtended by 2 bracts ....................................... grasses (Echinochloa, Glyceria spp., Leerzia oryzoides, Torreyochloa pallida, Zizania aquatica), p. 79
I. individual flowers of the inflorescence not subtended by bracts
M. flowers perfect ................ bayonet rush (Juncus militaris), p. 102
M. flowers unisexual
N. flowers in a dense, elongate spike; leaves flat .......................................................... cat-tail (Typha spp.), p. 71
N. flowers in spherical heads; leaves keeled, at least at the base .................................... bur-reed (Sparganium spp.), p. 61
A. emergent leaves broad, their blades less than 7 times longer than broad
O. plants woody at the base; branches arching over the water’s edge ............................................................ water-willow (Decodon verticillatus), p. 137
O. plants herbaceous throughout
P. leaves very large, roundish, often 30 cm or more across .................................................................................... lotus (Nelumbo spp.), p. 147
P. leaves never more than 20 cm across
Q. leaves compound
R. leaves opposite ............ beggar-ticks/bur-marigold (Bidens), p. 42
R. leaves alternate
S. plants to 2 m tall; leaflets toothed ................................................................ water-parsnip (Sium suave), p. 128
S. plants seldom more than 0.5 m tall; leaflets entire ..................................................... watercress (Nasturtium officinale), p. 141
Q. leaves simple
T. leaves opposite ....................... beggar-ticks/bur-marigold (Bidens), p. 42
T. leaves alternate
U. leaf blades lobed or truncate at the base
V. leaves kidney-shaped, mostly broader than long .................................................................. mud-plantain (Heteranthera spp.), p. 96
V. leaves longer than broad
W. leaf blades shallowly lobed, cordate, or truncate at the base
X. inflorescence a spike ............................................................................. lizard’s-tail (Saururus cernuus), p. 94
X. inflorescence a panicle .................................................................................... water-plantain (Alisma spp.), p. 129
W. leaf blades deeply lobed at base
Y. inflorescence a dense fleshy spike enclosed in a sheathing bract .............................................................................. arrow-arum (Peltandra virginica), p. 29
Y. inflorescence not enclosed in a sheathing bract
Z. flowers purple ............................................................................. pickerel-weed (Pontederia cordata), p. 100
Z. flowers white ........ arrowhead (Sagittaria spp.), p. 31
U. leaf blades tapering at both ends
AA. leaves parallel-veined; inflorescence a thick spike of yellow flowers ...................... goldenclub (Orontium aquaticum), p. 77
AA. leaves net-veined; inflorescence various
BB. emergent leaves toothed or lobed .......... mermaid-weed (Proserpinaca spp.), p. 273
BB. emergent leaves entire
CC. emergent leaves 2–5 mm long
DD. flowers unisexual, petals absent ......................... water-starwort (Callitriche terrestris), p. 229
DD. flowers bisexual, petals white .................................. Nuttall’s mud-flower (Micranthemum micranthemoides), p. 14
CC. emergent leaves more than 5 mm long
EE. inflorescence spike-like .................................................................... smartweed (Persicaria spp.), p. 104
EE. inflorescence not spike-like
FF. flowers yellow; fruits 2 cm or more long ............ water-primrose or primrose-willow (Ludwigia spp.), p. 132
FF. flowers pale violet to white or inconspicuous
GG. flowers small, inconspicuous, radially symmetrical; leaves ovate to obovate....water-purslane (Ludwigia palustris), p. 136
GG. flowers pale violet to white, 2-lipped; leaves linear to lanceolate ................. water-willow (Justicia americana), p. 137
Key to Floating-leaf Plants
A. leaves strap-like or ribbon-like, mostly submerged, floating only at the tips
B. midvein more prominent than the other veins of the leaf, cross veins not visible ............................................. bur-reed (Sparganium spp.), p. 61
B. midvein not more prominent than the other veins of the leaf, cross veins conspicuous ........................... water-celery (Vallisneria americana), p. 253
Figure 2.3. Leaf venation with and without prominent mid-vein.
A. leaves not strap-like, entire blade floating
C. floating leaves compound, shaped like a four-leaf clover ....................................................................... European water-clover (Marsilea quadrifolia), p. 151
C. floating leaves simple
D. floating leaves deeply notched or lobed at base of blade, or petiole attached near center of blade
E. petiole attached near the center of the blade
F. leaves very large, roundish, often 30 cm or more across ......................................................................... lotus (Nelumbo spp.), p. 147
F. leaves elliptical to linear-elliptic, never more than 20 cm across
G. floating leaves linear-elliptic, to about 2 cm long .................................................................... fanwort (Cabomba caroliniana), p. 272
G. floating leaves elliptic, 10–15 cm long ....................................................................... watershield (Brasenia schreberi), p. 161
E. petiole attached at the summit of a deep notch or sinus
H. flowers borne singly .................................................................. water-lily (Nuphar spp. and Nymphaea spp.), p. 153
H. flowers in an umbel ................. floating-heart (Nymphoides spp.), p. 143
D. floating leaves not deeply notched or lobed at base, petiole attached near base of blade
I. floating leaves in a rosette
J. leaf blades more than 2 cm long, petioles swollen in the middle .................................. European water-chestnut (Trapa natans), p. 149
J. leaf blades less than 2 cm long, petioles not swollen ............................................................... water-starwort (Callitriche spp.), p. 229
I. floating leaves borne singly
K. veins of the leaf blade parallel ................................................................ pondweed (Potamogeton spp.), p. 186
K. veins of the leaf blade netted
L. floating or emersed leaves generally kidney-shaped, 3-to 5-lobed ................... water-crowfoot (Ranunculus spp.), p. 275
L. floating or emersed leaves lance-shaped to elliptical, not lobed
M. floating or emersed leaves toothed ....................................................................... Beck’s water-marigold (Bidens beckii), p. 278
M. floating or emersed leaves entire ........................................................................... smartweed (Persicaria amphibia), p. 104
Key to Thalloid or Tiny Floating Plants
A. plants without distinguishable leaves and stems
B. plants appearing to consist entirely of repeatedly branching fine stems or stem-like structures ....... Charophyte algae (Chara spp. or Nitella spp.), p. 164
B. plants consisting entirely of flattened stems or segments
C. plants segmented, individual segments elliptical or rounded, solitary or in small clusters, or attached by strap-like stalks ............................................................................. duckweed, watermeal, and water flaxseed, p. 166
C. plants forming branching colonies of flattened stems
D. plants attached to rocks in fast-flowing water ................................................................ riverweed (Podostemum ceratophyllum), p. 180
D. plants free-floating .................................................................. aquatic liverworts (Riccia spp. or Ricciocarpus spp.), p. 163
A. plants with minutely leafy stems ...................................................................................... eastern mosquito fern (Azolla caroliniana), p. 178
Key to Submergent Leafy-stemmed Plants
A. leaves scale-like, or stems leafless
B. stems stiffly erect, leafless or with scattered, scale-like leaves ........................................................................ water-milfoil (Myriophyllum tenellum), p. 289
B. stems flexuous, more regularly leafy ...................................................................................... aquatic mosses (Fontanalis spp. or Sphagnum spp.), p. 183
A. leaves not scale-like
C. submersed leaves alternate
D. leaves with a basal sheath or sheathing stipules variously fused to the leaf base or free; flowers in a terminal or axillary spike; tepals 4, inconspicuous .............................................. pondweed (Potamogeton spp.), p. 186
D. leaves without basal sheaths or stipules; flowers terminal; tepals 6, yellow and conspicuous ......................... water star-grass (Heteranthera dubia), p. 221
C. submersed leaves opposite or whorled
E. leaves not more than 0.5 mm wide .......................................................................................... pondweed (Zannichellia palustris), p. 220
E. leaves more than 0.5 mm wide
F. leaves whorled
G. leaves mostly in whorls of 3............ waterweed (Elodea spp.), p. 233
G. leaves mostly in whorls of 4–8
H. leaf margins very finely toothed; leaves crowded, overlapping ............................................................ Brazilian waterweed (Egeria densa), p. 233
H. leaf margins distinctly spine-toothed; leaves not overlapping ............................................................ hydrilla (Hydrilla verticillata), p. 185
F. leaves opposite
I. leaves with a narrow blade and a broader, sheathing base ................................................................................. waternymph (Najas spp.), p. 223
I. leaves tapering or truncate at the base, broadest in the blade
J. leaves linear, spatulate, or obovate, weakly 3-nerved ................................................................................ water-starwort (Callitriche spp.), p. 229
J. leaves oblong to narrowly obovate, 0–1-nerved ....................................................................................... waterwort (Elatine spp.), p. 237
Figure 2.4. Leaf arrangement in waterweeds (not to scale).
Key to Submergent Rosette-forming Plants
A. leaves strongly flattened
B. leaves mostly more than 20 times longer than wide
C. midvein not more prominent than the other veins of the leaf; cross veins conspicuous
D. cross veins in the central portion of leaves more densely reticulate .............................. water-celery (Vallisneria americana), p. 253
Figure 2.5. Vein reticulation (not to scale).
D. reticulate network of cross veins uniform throughout the leaf .................................................................. arrowhead (Sagittaria spp.), p. 31
C. midvein more prominent than the other veins of the leaf; cross veins not readily visible ................................ bur-reed (Sparganium spp.), p. 61
B. leaves less than 20 times longer than wide
E. plants mat-forming
F. leaves acute at the tips .......................... pipewort (Eriocaulon spp.), p. 243
F. leaves rounded at the tips
G. leaves to about 2 cm long, in pairs along the stolons ....................................................................... mudmat (Glossostigma cleistanthum), p. 241
G. leaves mostly 2–5 cm long, in tufts of 5–10 along the stolons ................................................................. mudwort (Limosella australis), p. 14
E. plants not mat-forming
H. leaves rounded at the tips ....... water lobelia (Lobelia dortmanna), p. 251
H. leaves acute at the tips ................................ pipewort (Eriocaulon spp.), p. 243
A. leaves generally round in cross section, not strongly flattened, or leaves absent, only stems apparent
I. leaves or stems stiff and firm, holding their shape out of water
J. leaf bases expanded and containing spore sacs .................................................................................... quillwort (Isoetes spp.), p. 245
J. leaf or stem bases not containing spore sacs .......................................................................................................... spike-rush (Eleocharis spp.), p. 111
I. leaves or stems limp, not holding their shape out of water
K. leaves reduced to bladeless sheaths at the base of the stems; flowering stems with a single terminal spikelet....spike-rush (Eleocharis spp.), p. 111
K. basal leaves filamentous; flowering stems lacking a basal sheath, each bearing a single lateral spikelet .... bulrush (Schoenoplectus subterminalis). p. 53
Figure 2.6. Quillwort leaf with spore sac in the base (×3/8).
Figure 2.7. Bladeless leaf sheaths in a spike-rush (Eleocharis sp., ×1/4).
Key to Submergent Plants with Finely Divided Leaves
A. leaves and/or stems bearing small bladders ................................................................................................... bladderwort (Utricularia spp.), p. 255
A. leaves and/or stems not bearing bladders
B. leaves opposite or whorled
C. leaves pinnately divided ............... water-milfoil (Myriophyllum spp.), p. 280
C. leaves palmately divided, fan-like; the segments repeatedly forking
D. leaves remaining rigid out of water, often crowded toward the stem tips ................................................. coontail (Ceratophyllum spp.), p. 269
D. leaves limp out of water, not crowded toward the stem tips
E. submersed leaves with a distinct petiole; flowers white ............................................................ fanwort (Cabomba caroliniana), p. 272
E. submersed leaves without a distinct petiole; flowers yellow ............................................................ Beck’s water-marigold (Bidens beckii), p. 278
B. leaves alternate
F. underwater leaves pinnately divided; simple emergent leaves often present ............................................. mermaid-weed (Proserpinaca spp.), p. 273
F. underwater leaves palmately divided, fan-like; the segments repeatedly forking; emergent leaves never present ........................................................................... water-crowfoot (Ranunculus spp.), p. 275
Figure 2.8. Leaf form and arrangement (not to scale).
