smaller, specialized structures that are more tolerant of freezing and desiccation. Categorized
as turions (Landolt 1986), these unusual structures actually represent modified whole plants
(Sculthorpe 1967) and often are induced under
periods of nutrient deficiency or attenuating
daylight (Landolt and Kandeler 1987).
Duckweeds also are capable of sexual reproduction, which is accomplished via tiny flowers
that self-pollinate, or are pollinated above the
water surface by small arthropod vectors such as
aphids, flies, mites, and spiders; despite some
reports to the contrary, they are not
water-pollinated (Landolt 1986, 1992a, b). Most
species produce only one tiny seed per ovary
(Landolt 1986). Duckweed fronds range in size
from 0.5 to 15 mm in length, with the miniscule
members of the genus Wolffia representing the
smallest of all angiosperm species.
Duckweeds evolved from an ancestor that
likely resembled modern aroid plants (e.g.,
Arisaema, Calla, Orontium, Philodendron), and
they diversified into 37 currently recognized
species (Table 2.1; Cabrera et al. 2008;
Cusimano et al. 2011; Nauheimer et al. 2012;
Sree et al. 2016). The five genera are rather easily
distinguished using vegetative features: Landoltia (dotted duckmeat) and Spirodela (duckmeat) species have relatively large, floating
fronds each with multiple roots; Lemna (duckweed) fronds are mostly floating (except for the
suspended L. trisulca) with one root each;
Wolffia (watermeal) species have small and stout
fronds lacking roots; and Wolffiella (mudmidget)
plants also lack roots and have small, elongated
fronds. (In this chapter, we will use the term
“duckweed” to refer broadly to plants in the
family Lemnaceae, although this common name
sometimes is used more specifically to refer only
to members of the genus Lemna.) Ecologically,
duckweeds are an important component of
aquatic habitats: They grow densely and shade
out large portions of shallow, still water
(Sculthorpe 1967; Landolt 1986; Parr et al. 2002;
Roijackers et al. 2004; Driever et al. 2005), and
are an important food source for waterfowl, fish,
and other herbivores (Sculthorpe 1967; Rusoff
et al. 1980).
Duckweed plants are distributed in temperate
and tropical latitudes worldwide (Landolt 1986).
In temperate environments, they may produce
turions or rely more heavily upon seeds to survive colder winter temperatures (Crawford et al.
2006). They are able to disperse rather easily as
seeds or fronds, because their small size enables
them to adhere to the legs and feathers of
waterfowl (Jacobs 1947; Hillman 1961; Landolt
1986; Les et al. 2003; Coughlan et al. 2014,
2017; Green 2016). Duckweeds frequently
reproduce vegetatively, and flowering, when it
occurs, may be influenced by day length
(Hillman 1976).
Duckweeds have become recognized in recent
years for their potential applications in biofuels,
environmental remediation, carbon sequestration,
and biochemical production (Bonomo et al.
1997; Stomp 2005; Cheng and Stomp 2009; Ge
et al. 2012; Xu et al. 2012; Su et al. 2014; Cui
and Cheng 2015). They are capable of rather
rapid vegetative multiplication, require minimal
nutrients (Lasfar et al. 2007), are readily cultured
(e.g., Oron 1994), and are amenable to genetic
manipulation (Yamamoto et al. 2001; CantóPastor et al. 2015). Besides their potential
applications for human benefit, duckweeds also
offer a study system in which to investigate
ecological and evolutionary questions (Crawford
et al. 2006; Laird and Barks 2018). Although a
few species (e.g., Lemna gibba, Spirodela polyrhiza) have received the most study, the diversity
of Lemnaceae could enable more varied research
applications in the future.
2.2 Taxonomy
Currently, there are 13 accepted species of
Lemna, 11 species of Wolffia, ten of Wolffiella,
two species of Spirodela, and one of Landoltia,
for a total of 37 duckweed species worldwide
(Sree et al. 2016; Table 2.1). The first duckweed
species to be recognized by Linnaeus (1753) all
were classified within the single genus Lemna.
Authors subsequently segregated species among
Wolffia (named originally by Schreber in 1791,
but not validly published until Schleiden in
20
N. P. Tippery and D. H. Les
as turions (Landolt 1986), these unusual structures actually represent modified whole plants
(Sculthorpe 1967) and often are induced under
periods of nutrient deficiency or attenuating
daylight (Landolt and Kandeler 1987).
Duckweeds also are capable of sexual reproduction, which is accomplished via tiny flowers
that self-pollinate, or are pollinated above the
water surface by small arthropod vectors such as
aphids, flies, mites, and spiders; despite some
reports to the contrary, they are not
water-pollinated (Landolt 1986, 1992a, b). Most
species produce only one tiny seed per ovary
(Landolt 1986). Duckweed fronds range in size
from 0.5 to 15 mm in length, with the miniscule
members of the genus Wolffia representing the
smallest of all angiosperm species.
Duckweeds evolved from an ancestor that
likely resembled modern aroid plants (e.g.,
Arisaema, Calla, Orontium, Philodendron), and
they diversified into 37 currently recognized
species (Table 2.1; Cabrera et al. 2008;
Cusimano et al. 2011; Nauheimer et al. 2012;
Sree et al. 2016). The five genera are rather easily
distinguished using vegetative features: Landoltia (dotted duckmeat) and Spirodela (duckmeat) species have relatively large, floating
fronds each with multiple roots; Lemna (duckweed) fronds are mostly floating (except for the
suspended L. trisulca) with one root each;
Wolffia (watermeal) species have small and stout
fronds lacking roots; and Wolffiella (mudmidget)
plants also lack roots and have small, elongated
fronds. (In this chapter, we will use the term
“duckweed” to refer broadly to plants in the
family Lemnaceae, although this common name
sometimes is used more specifically to refer only
to members of the genus Lemna.) Ecologically,
duckweeds are an important component of
aquatic habitats: They grow densely and shade
out large portions of shallow, still water
(Sculthorpe 1967; Landolt 1986; Parr et al. 2002;
Roijackers et al. 2004; Driever et al. 2005), and
are an important food source for waterfowl, fish,
and other herbivores (Sculthorpe 1967; Rusoff
et al. 1980).
Duckweed plants are distributed in temperate
and tropical latitudes worldwide (Landolt 1986).
In temperate environments, they may produce
turions or rely more heavily upon seeds to survive colder winter temperatures (Crawford et al.
2006). They are able to disperse rather easily as
seeds or fronds, because their small size enables
them to adhere to the legs and feathers of
waterfowl (Jacobs 1947; Hillman 1961; Landolt
1986; Les et al. 2003; Coughlan et al. 2014,
2017; Green 2016). Duckweeds frequently
reproduce vegetatively, and flowering, when it
occurs, may be influenced by day length
(Hillman 1976).
Duckweeds have become recognized in recent
years for their potential applications in biofuels,
environmental remediation, carbon sequestration,
and biochemical production (Bonomo et al.
1997; Stomp 2005; Cheng and Stomp 2009; Ge
et al. 2012; Xu et al. 2012; Su et al. 2014; Cui
and Cheng 2015). They are capable of rather
rapid vegetative multiplication, require minimal
nutrients (Lasfar et al. 2007), are readily cultured
(e.g., Oron 1994), and are amenable to genetic
manipulation (Yamamoto et al. 2001; CantóPastor et al. 2015). Besides their potential
applications for human benefit, duckweeds also
offer a study system in which to investigate
ecological and evolutionary questions (Crawford
et al. 2006; Laird and Barks 2018). Although a
few species (e.g., Lemna gibba, Spirodela polyrhiza) have received the most study, the diversity
of Lemnaceae could enable more varied research
applications in the future.
2.2 Taxonomy
Currently, there are 13 accepted species of
Lemna, 11 species of Wolffia, ten of Wolffiella,
two species of Spirodela, and one of Landoltia,
for a total of 37 duckweed species worldwide
(Sree et al. 2016; Table 2.1). The first duckweed
species to be recognized by Linnaeus (1753) all
were classified within the single genus Lemna.
Authors subsequently segregated species among
Wolffia (named originally by Schreber in 1791,
but not validly published until Schleiden in
20
N. P. Tippery and D. H. Les