The Jepson Herbarium
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Perennial herb, [shrub, vine], terrestrial [growing on other plants or not], or aquatic, sometimes free-floating, then sometimes much reduced, in dense, clonal populations, 0.4–10 mm, flat and tongue-shaped to spheric, not differentiated into stems and leaves, new plants produced in budding pouch at base or along margins, sometimes overwintering on bottom as dense, rootless, starch-filled daughter plant (winter bud); often from short, generally erect caudex; roots 0–many; often monoecious. Stem: sometimes above ground in addition to caudex, or not differentiated from plant body. Leaf: simple or compound, basal (or cauline, 2-ranked), or not differentiated from plant body. Inflorescence: generally spike, fleshy, generally ill-smelling, or flower 1, rarely seen, minute, appearing like 2–3 unisexual flowers, often sheathed by minute membrane; flowers bisexual or pistillate below, staminate above; bract subtending spike 1, generally showy (petal-like), generally > spike, sheathing or not. Flower: perianth parts 0, 4, 6, free or fused; stamens 0–4, 6, free or fused; ovary superior to 1/2-inferior and sunken in inflorescence axis, chambers 1–3, stigma ± sessile. Fruit: berry or achene-like, winged or not. Seed: 1–many, often ribbed.
± 114 genera, 1850 species: generally tropics, subtropics some cultivated for food, ornamental in ponds, aquaria (Colocasia, taro) or ornamental (Philodendron, Anthurium). [Les et al. 2002 Syst Bot 27:221–240; Thompson 2000 FNANM 22:128–142] Since TJM (1993), including Lemnaceae, and except Acorus, now in Acoraceae (the sole member in California, Acorus calamus L., is an historical waif). Pistia stratiotes L. <WEEDINESS: SYMBOL 1> is a waif. Pinellia ternata (Thunb.) Breitenbach possibly naturalized in California. In taxa once included in Lemnaceae, vein number per plant body best determined using backlight. —Scientific Editors: Bruce G. Baldwin, Thomas J. Rosatti.
Unabridged references: [Armstrong, http://waynesword.palomar.edu/1wayindx.htm; Stockey et al. 1997 Amer J Bot 84:355–368; Les et al. 2002 Syst Bot 27(2):221–240]
Unabridged note: Since TJM (1993), including Lemnaceae, except Acorus, now in Acoraceae (the sole representative of the family in California, Acorus calamus, judged to be an historical waif in California and therefore here except). Incl smallest of all known angiosperms (Wolffia globosa) as well as world's most massive inflorescence (spike of Amorphophallus titanum, Titan Arum, to 4 m in circumference). Needle-like crystals in most tissues cause intense irritation when chewed; those of Dieffenbachia, dumb-cane, may induce temporary speechlessness. Incl of fossil evidence in cladistic analyses indicate Lemnaceae and Pistia form a monophyletic group within Araceae (Stockey et al.), a position now generally accepted (see Les et al.). Pinellia ternata (Thunb.) Makino ex Breitenbach introduced, possibly naturalized in California. Taxa formerly included in Lemnaceae may be very invasive. In taxa formerly included in Lemnaceae, vein number per plant body best determined using backlight. Peltandra virginica (L.) Schott & Endl., included in TJM (1993), reportedly spread from ornamental pool introduction in 1970 to nearby reserviors, but degree of reproduction or even persistence there unknown.

Key to Araceae

1. Plants not reduced, clearly differentiated into stems, leaves; floating aquatics or not; inflorescence a spike, conspicuous; perianth parts 0, 4, 6; stamens 0, 2, 3, 4, 6 (genera treated as Araceae in TJM (1993), minus Acorus)

2. Plant aquatic, floating; inflorescence ± sessile, inconspicuous among basal leaves ..... [PISTIA]

2' Plant terrestrial or near edge of water; inflorescence peduncled, ± conspicuous

3. Petiole < leaf blade; inflorescence bract yellow ..... LYSICHITON

3' Petiole ± >= leaf blade; inflorescence bract sometimes pale yellow-green but not yellow

4. Peduncle ± >= leaf; inflorescence bract white both surfaces (tip generally pale green) ..... ZANTEDESCHIA

4' Peduncle generally << leaf; inflorescence bract abaxially pale yellow-green, adaxially ± white to pale yellow-green or dark purple, or green both surfaces (margins pale green to white or not)

5. Inflorescence sterile in ± upper 1/2, flowers only in lower 1/2; inflorescence bract abaxially pale yellow-green, adaxially ± white to pale yellow-green or dark purple ..... ARUM

5' Inflorescence fertile throughout; inflorescence bract green both surfaces (margins pale green to white or not) ..... [Peltandra virginica]

1' Plants much reduced, not differentiated into stems, leaves; floating aquatics; inflorescence 1-flowered, inconspicuous; perianth parts 0; stamens 1, 2 (genera treated as Lemnaceae in TJM (1993))

6. Roots 0 (see also Lemna trisulca)

7. Plant body ± cylindric to nearly spheric, 0.4–1.3 mm ..... WOLFFIA

7' Plant body flat, linear to oblong, 3–10 mm ..... WOLFFIELLA

6' Roots present

8. Root generally 1 ..... LEMNA

8' Roots generally 2–16

9. Roots generally 2–7; plant body 3–5 mm, veins 3–7; winter buds 0 ..... LANDOLTIA

9' Roots generally 7–16; plant body 5–10 mm, veins 7–12; winter buds produced ..... SPIRODELA

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Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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