in its vegetative phase (Landolt 1980, 1986; Sree
et al. 2015c). Although duckweeds are angiosperms, their dominant reproductive strategy is via
vegetative propagation. A daughter frond buds
from the vegetative pouch of a mother frond, thus
forming a colony of plants having the same
genetic structure. The plants of such a colony and
their progeny (by vegetative propagation) are
called to be a clone of a particular species. So, the
plants with the same species identity, collected
from different geographical locations, which
might have been adapted to grow in different
climatic conditions, can be cultured as different
clones (Bog et al. 2018). These clones constitute
the rich genetic resource of duckweeds.
Apart from the enthusiasm of the researchers
to study some of the basic questions of plant
biology using duckweeds as model plants, these
plants are also a treasure for the entrepreneurs.
Duckweeds, in view of their physiological and
biotechnological properties, are used in a wide
array of practical applications (Appenroth et al.
2015). The high nutritious value of duckweeds
makes it a good food and feed supplement for
humans (Appenroth et al. 2017, 2018), fish, cattle, poultry and so on (Landolt and Kandeler
1987). Depending on the growth conditions,
duckweeds can be modulated to accumulate high
amounts of starch, which finds use in the bioenergy field (Cui and Cheng 2015; Ma et al. 2018).
Other applications of duckweed include biomass
production, wastewater treatment (Ziegler et al.
2018), biotechnological uses in the pharmaceutical industry and so on (Appenroth et al. 2015).
Through numerous research studies conducted
worldwide, it is evident that the physiological
properties of duckweed are not dependent on the
species but on the clones of duckweed collected
from different geographical locations and so are
the relevant practical applications. Some of the
physiological properties which have been tested
include growth rate (Sree et al. 2015a; Ziegler
et al. 2015), turion formation (Kuehdorf et al.
2013), starch accumulation capacity (Sree et al.
2015c; Ma et al. 2018) and protein content
(Appenroth et al. 2018). Hence, over the years, it
became extremely important to study several
clones of the same species collected from
different geographical locations, in order to
understand better the biodiversity, genetics and
the inherent potential of duckweeds. For a
researcher to travel to different places in order to
collect different clones and decipher their species
identity cannot only be expensive but is also time
consuming and requires expertise in the field. In
this respect, the duckweed clonal stock collections that are repositories of duckweed genetic
resources help other researchers to have access to
clones of different duckweed species.
3.2 Duckweed: Genera and Species
As of now, in the family Lemnaceae, 36 different
species of duckweed have been identified and
taxonomically categorized into five genera (Sree
et al. 2016; Bog et al. 2020a, b) (Figs. 3.1 and
3.2). Based on their morphology, they have been
categorized into two subfamilies: Lemnoideae
and Wolffioideae. The Lemnoideae possess roots
and have two lateral pouches from where new
fronds are vegetatively produced. The Wolffioideae, on the other hand, have only one such
pouch and are devoid of roots (Landolt 1986; Les
et al. 2002). The complete botanical names and
recent changes in nomenclature of all the currently accepted species were given by Sree et al.
(2016) and Bog et al. (2020a, b). Very recently,
the total number of duckweed species was
reduced from 37 to 36 (Bog et al. 2020a, b).
3.3 Duckweed Stock Collection: The
Pioneer
The late Elias Landolt evidently realized the
importance of duckweed clones grown under different climatic conditions, and during his stay as a
young post-doc at the Stanford University, CA,
from 1953 to 1955, he had started collecting
duckweed plants from widespread geographical
locations, which grew into the Landolt Duckweed
Collection at Zurich, Switzerland, with numerous
duckweed clones collected from around the globe.
E. Landolt added these collected duckweed plants
to an already existing non-duckweed plant
40
K. S. Sree and K.-J. Appenroth
et al. 2015c). Although duckweeds are angiosperms, their dominant reproductive strategy is via
vegetative propagation. A daughter frond buds
from the vegetative pouch of a mother frond, thus
forming a colony of plants having the same
genetic structure. The plants of such a colony and
their progeny (by vegetative propagation) are
called to be a clone of a particular species. So, the
plants with the same species identity, collected
from different geographical locations, which
might have been adapted to grow in different
climatic conditions, can be cultured as different
clones (Bog et al. 2018). These clones constitute
the rich genetic resource of duckweeds.
Apart from the enthusiasm of the researchers
to study some of the basic questions of plant
biology using duckweeds as model plants, these
plants are also a treasure for the entrepreneurs.
Duckweeds, in view of their physiological and
biotechnological properties, are used in a wide
array of practical applications (Appenroth et al.
2015). The high nutritious value of duckweeds
makes it a good food and feed supplement for
humans (Appenroth et al. 2017, 2018), fish, cattle, poultry and so on (Landolt and Kandeler
1987). Depending on the growth conditions,
duckweeds can be modulated to accumulate high
amounts of starch, which finds use in the bioenergy field (Cui and Cheng 2015; Ma et al. 2018).
Other applications of duckweed include biomass
production, wastewater treatment (Ziegler et al.
2018), biotechnological uses in the pharmaceutical industry and so on (Appenroth et al. 2015).
Through numerous research studies conducted
worldwide, it is evident that the physiological
properties of duckweed are not dependent on the
species but on the clones of duckweed collected
from different geographical locations and so are
the relevant practical applications. Some of the
physiological properties which have been tested
include growth rate (Sree et al. 2015a; Ziegler
et al. 2015), turion formation (Kuehdorf et al.
2013), starch accumulation capacity (Sree et al.
2015c; Ma et al. 2018) and protein content
(Appenroth et al. 2018). Hence, over the years, it
became extremely important to study several
clones of the same species collected from
different geographical locations, in order to
understand better the biodiversity, genetics and
the inherent potential of duckweeds. For a
researcher to travel to different places in order to
collect different clones and decipher their species
identity cannot only be expensive but is also time
consuming and requires expertise in the field. In
this respect, the duckweed clonal stock collections that are repositories of duckweed genetic
resources help other researchers to have access to
clones of different duckweed species.
3.2 Duckweed: Genera and Species
As of now, in the family Lemnaceae, 36 different
species of duckweed have been identified and
taxonomically categorized into five genera (Sree
et al. 2016; Bog et al. 2020a, b) (Figs. 3.1 and
3.2). Based on their morphology, they have been
categorized into two subfamilies: Lemnoideae
and Wolffioideae. The Lemnoideae possess roots
and have two lateral pouches from where new
fronds are vegetatively produced. The Wolffioideae, on the other hand, have only one such
pouch and are devoid of roots (Landolt 1986; Les
et al. 2002). The complete botanical names and
recent changes in nomenclature of all the currently accepted species were given by Sree et al.
(2016) and Bog et al. (2020a, b). Very recently,
the total number of duckweed species was
reduced from 37 to 36 (Bog et al. 2020a, b).
3.3 Duckweed Stock Collection: The
Pioneer
The late Elias Landolt evidently realized the
importance of duckweed clones grown under different climatic conditions, and during his stay as a
young post-doc at the Stanford University, CA,
from 1953 to 1955, he had started collecting
duckweed plants from widespread geographical
locations, which grew into the Landolt Duckweed
Collection at Zurich, Switzerland, with numerous
duckweed clones collected from around the globe.
E. Landolt added these collected duckweed plants
to an already existing non-duckweed plant
40
K. S. Sree and K.-J. Appenroth