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ARACEAE ARUM FAMILY

Thomas J. Rosatti, except as noted

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. <{Noxious weed}> 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

LEMNA DUCKWEED

Wayne P. Armstrong

Plants much reduced, not differentiated into stems, leaves; floating aquatic; root generally 1, generally 2–6 mm, sheath near base generally not winged. Plant body: generally in 2s to 8s; generally 2–5 mm, flat, generally widely elliptic to oblong, pale to dark green, often ± red; veins 1–5; winter buds generally 0. Inflorescence: flowers in 2 lateral pouches, sheathed by minute membrane. Fruit: generally unwinged. Seed: ribbed, generally smooth between ribs.
14 species: worldwide. (Greek: lake or swamp) Lemna obscura (Austin) Daubs. [Lemna minor L. var. obscura Austin] excluded.

Key to Lemna

L. trisulca L.
NATIVE
Root often 0. Plant body: often in branched chains of 8–30, on tapered stalk; 6–10 mm, lanceolate to oblong, transparent green, base, tip symmetric, surfaces smooth.
Meadows, mountain streams; < 3000 m. Cascade Range, Sierra Nevada, Sacramento Valley, San Bernardino Mountains, Great Basin Floristic Province, Modoc Plateau, Mojave Desert; ± worldwide. Generally forming dense, tangled masses below water surface. Aug [Online Interchange]

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Citation for the whole project: Jepson Flora Project (eds.) 2013. Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html, accessed on Apr 23 2014
Citation for this treatment: [Author of taxon treatment] 2012. Lemna, in Jepson Flora Project (eds.) Jepson eFlora, http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?tid=30466, accessed on Apr 23 2014

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Bioregions in which Lemna trisulca occurs Markers link to CCH specimen records. If the markers are obscured, reload the page [or change window size and reload]. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.