grew in North America (14.3–34.8 Ma), from
which L. aequinoctialis expanded its range to
become cosmopolitan (c. 4.4 Ma) and L. tenera
dispersed to Southeast Asia (c. 14.3 Ma;
Fig. 2.2b). Section Lemna includes several species with broad geographic ranges (Fig. 2.2c),
and the common ancestor of the section was
reconstructed to inhabit North America (16.4–
41.7 Ma). The ancestor of Wolffioideae likely
grew in the Americas also (24.4–54.4 Ma). The
phylogenetically ambiguous Wolffia species
either remained in the Americas (W. borealis, W.
brasiliensis) or dispersed independently to Australia (W. australiana) or eastern Asia (W.
microscopica) (all dispersals of these species
were reconstructed to have occurred roughly
19.2–22.5 Ma). The geographic range for the
common ancestor of section Wolffia was uncertain, with the reconstruction more strongly supporting ancestral areas that included Africa or
eastern Asia (8.0–19.8 Ma). The common
ancestor of W. angusta, W. globosa, and
W. neglecta, however, resolved rather clearly as
east Asian or Australian (4.6–8.0 Ma), regions
where these species grow today. Likewise, the
sibling species W. arrhiza and W. cylindracea
had an ancestor in Africa (4.5–6.9 Ma) where
both species are found today, and the ancestor of
the sibling species W. columbiana and W. elongata likely dispersed to South America
(3.7–6.9 Ma) where these species grow today.
Our biogeographic reconstruction for Wolffiella
supported the analyses done by Kimball et al.
(2003) and placed the common ancestor of the
genus in Africa (15.6–22.5 Ma), where W. denticulata, some populations of W. welwitschii, and
species in sections Rotundae and Stipitatae grow
today. Starting about 3.9–9.7 Ma and possibly
coincident with the range expansion of W. welwitschii, the ancestor of W. caudata, W. gladiata,
W. lingulata, W. neotropica, and W. oblonga
dispersed into the Americas.
Anthropogenic dispersal events have been
responsible for the recent introductions of some
species. Lemna minuta, native to the Americas, is
invasive in Europe and Japan (Landolt 2000;
Ceschin et al. 2017). Landoltia punctata has a
rather large native range, including Africa,
Southeast Asia, Australia, and South America,
and in the modern era, it has expanded into
Europe and North America (Landolt 1986; Les
et al. 1997; Jacono 2018). Other anthropogenic
duckweed dispersal events include L. gibba to
Japan and L. minor to Australasia (Landolt
1986). Given their abundance and capacity for
dispersal, duckweeds represent a likely group of
plants for colonizing new territory, potentially
aided by humans.
2.6 Conclusions
Many aspects that make Lemnaceae distinct,
from their profound morphological evolution to
their extensive geographical dispersal capacity,
are enlightened by having a phylogenetic perspective. Duckweeds for the most part have a
stable and well-resolved phylogeny that allows
for meticulous reconstruction of ancestral morphological states and biogeography. Only a
handful of Wolffia species remain ambiguously
resolved on the molecular phylogeny, and future
genomic-level phylogenetic studies may soon
resolve these species satisfactorily. Genomic
sequence data also stand to offer new perspectives into the unique physiology of duckweeds,
and molecular biotechnology may be able to
deliver duckweed strains that are maximally
productive for biofuel production, wastewater
remediation, or other applications. Amid all of
the potential new benefits from studying duckweeds, it will be important to retain a phylogenetic perspective, for example, to explore
enzyme variants or similar physiological pathways in related species. Individual duckweed
species each contain a wealth of biological
potential, and taken together, the Lemnaceae are
an extensive resource for biotechnology.
Acknowledgements We are grateful to Daniel J. Crawford for reviewing the novel biogeographical research
presented here and to Paul Fourounjian, Wenqin Wang,
and Hieu Cao for editorial assistance.
34
N. P. Tippery and D. H. Les
which L. aequinoctialis expanded its range to
become cosmopolitan (c. 4.4 Ma) and L. tenera
dispersed to Southeast Asia (c. 14.3 Ma;
Fig. 2.2b). Section Lemna includes several species with broad geographic ranges (Fig. 2.2c),
and the common ancestor of the section was
reconstructed to inhabit North America (16.4–
41.7 Ma). The ancestor of Wolffioideae likely
grew in the Americas also (24.4–54.4 Ma). The
phylogenetically ambiguous Wolffia species
either remained in the Americas (W. borealis, W.
brasiliensis) or dispersed independently to Australia (W. australiana) or eastern Asia (W.
microscopica) (all dispersals of these species
were reconstructed to have occurred roughly
19.2–22.5 Ma). The geographic range for the
common ancestor of section Wolffia was uncertain, with the reconstruction more strongly supporting ancestral areas that included Africa or
eastern Asia (8.0–19.8 Ma). The common
ancestor of W. angusta, W. globosa, and
W. neglecta, however, resolved rather clearly as
east Asian or Australian (4.6–8.0 Ma), regions
where these species grow today. Likewise, the
sibling species W. arrhiza and W. cylindracea
had an ancestor in Africa (4.5–6.9 Ma) where
both species are found today, and the ancestor of
the sibling species W. columbiana and W. elongata likely dispersed to South America
(3.7–6.9 Ma) where these species grow today.
Our biogeographic reconstruction for Wolffiella
supported the analyses done by Kimball et al.
(2003) and placed the common ancestor of the
genus in Africa (15.6–22.5 Ma), where W. denticulata, some populations of W. welwitschii, and
species in sections Rotundae and Stipitatae grow
today. Starting about 3.9–9.7 Ma and possibly
coincident with the range expansion of W. welwitschii, the ancestor of W. caudata, W. gladiata,
W. lingulata, W. neotropica, and W. oblonga
dispersed into the Americas.
Anthropogenic dispersal events have been
responsible for the recent introductions of some
species. Lemna minuta, native to the Americas, is
invasive in Europe and Japan (Landolt 2000;
Ceschin et al. 2017). Landoltia punctata has a
rather large native range, including Africa,
Southeast Asia, Australia, and South America,
and in the modern era, it has expanded into
Europe and North America (Landolt 1986; Les
et al. 1997; Jacono 2018). Other anthropogenic
duckweed dispersal events include L. gibba to
Japan and L. minor to Australasia (Landolt
1986). Given their abundance and capacity for
dispersal, duckweeds represent a likely group of
plants for colonizing new territory, potentially
aided by humans.
2.6 Conclusions
Many aspects that make Lemnaceae distinct,
from their profound morphological evolution to
their extensive geographical dispersal capacity,
are enlightened by having a phylogenetic perspective. Duckweeds for the most part have a
stable and well-resolved phylogeny that allows
for meticulous reconstruction of ancestral morphological states and biogeography. Only a
handful of Wolffia species remain ambiguously
resolved on the molecular phylogeny, and future
genomic-level phylogenetic studies may soon
resolve these species satisfactorily. Genomic
sequence data also stand to offer new perspectives into the unique physiology of duckweeds,
and molecular biotechnology may be able to
deliver duckweed strains that are maximally
productive for biofuel production, wastewater
remediation, or other applications. Amid all of
the potential new benefits from studying duckweeds, it will be important to retain a phylogenetic perspective, for example, to explore
enzyme variants or similar physiological pathways in related species. Individual duckweed
species each contain a wealth of biological
potential, and taken together, the Lemnaceae are
an extensive resource for biotechnology.
Acknowledgements We are grateful to Daniel J. Crawford for reviewing the novel biogeographical research
presented here and to Paul Fourounjian, Wenqin Wang,
and Hieu Cao for editorial assistance.
34
N. P. Tippery and D. H. Les