Chapter 1
Taxonomy and Biogeography of Seagrasses
C. den Hartog*
Zevenheuvelenweg 50, 6571 CK, Berg en Dal, The Netherlands
John Kuo
Centre for Microscopy and Microanalysis, M010, The University of Western Australia,
35 Stirling Highway, Crawley, Western Australia 6009, Australia
I. Introduction
Seagrasses are aquatic angiosperms, which are confined to the marine environment. The term seagrass
(with several linguistic variants in the Germanic
language group) refers undoubtedly to the grasslike habit of most of its representatives. The term
has been long used by fisherman, hunters, farmers,
and other inhabitants of the coastal areas of several
European countries, i.e. areas where only species occur with long linear leaves. Ascherson (1871) probably was the first researcher to introduce the term
into the scientific literature.
The seagrasses form an ecological group, and not
a taxonomic group. This implies that the various seagrass families do not necessarily have to be closely
related.
The taxa regarded as seagrasses belong to a very
limited number of plant families, all classified within
the superorder Alismatiflorae (Monocotyledonae)
(Dahlgren et al., 1985), also generally known as
the Helobiae (Tomlinson, 1982). The subclass Alismatanae (Kubitzki, 1998) is with respect to its
contents identical with Alismatiflorae. Three out
of four families consist exclusively of seagrasses,
viz. the Zosteraceae, the Cymodoceaceae, and the
Posidoniaceae. In the past these families generally
have been classified as subfamilies of the Potamogetonaceae (Ascherson and Graebner, 1907; den
Hartog, 1970). Further studies have shown that
the latter family appeared to be too heterogeneous
(Tomlinson, 1982; Dahlgren et al., 1985), and had to
∗ Author for correspondence, email: c.denhartog@inter.nl.net
be split. So, apart from the Potamogetonaceae sensu
stricto, all of the former subfamilies were upgraded
to the family level. In fact some authors had already
long ago recognized the special identity of these
families, e.g. Dumortier who described the Zosteraceae as early as 1829 as an independent family
beside the Potamogetonaceae sensu stricto, and the
Zannichelliaceae. A fourth family, the Hydrocharitaceae, contains three genera that are considered
seagrasses, but the other 14 genera in this family are
confined to fresh-water habitats (Cook, 1990, 1998).
Apart from the families mentioned above which
have altogether 12 marine genera there are no other
genera that are fully confined to the marine environment. In other aquatic plant families so far only
two species have been found that occur exclusively in
marine habitats, viz. Ruppia aff. tuberosa of the family Ruppiaceae, and Lepilaena marina of the family Zannichelliaceae (Kuo and den Hartog, 2000).
The inclusion of these two species within the seagrasses is still a matter of debate. Descriptions of
these families and genera have been included in
the treatment of the monocotyledonous flowering
plants edited by Kubitzki (1998) (Hydrocharitaceae
by Cook; Ruppiaceae and Najadaceae by Haynes,
Holmberg-Nielsen and Les; Potamogetonaceae and
Zannichelliaceae by Haynes, Les and Holm-Nielsen;
Cymodoceaceae, Posidoniaceae and Zosteraceae by
Kuo and McComb). Furthermore, brief descriptions
of all presently described seagrass species, as well
as a key for the identification of them, have been
provided by Kuo and den Hartog (2001).
Arber (1920) formulated a set of four properties, which in her opinion were considered to be
c
1–23.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
2006 Springer. Printed in the Netherlands.
Taxonomy and Biogeography of Seagrasses
C. den Hartog*
Zevenheuvelenweg 50, 6571 CK, Berg en Dal, The Netherlands
John Kuo
Centre for Microscopy and Microanalysis, M010, The University of Western Australia,
35 Stirling Highway, Crawley, Western Australia 6009, Australia
I. Introduction
Seagrasses are aquatic angiosperms, which are confined to the marine environment. The term seagrass
(with several linguistic variants in the Germanic
language group) refers undoubtedly to the grasslike habit of most of its representatives. The term
has been long used by fisherman, hunters, farmers,
and other inhabitants of the coastal areas of several
European countries, i.e. areas where only species occur with long linear leaves. Ascherson (1871) probably was the first researcher to introduce the term
into the scientific literature.
The seagrasses form an ecological group, and not
a taxonomic group. This implies that the various seagrass families do not necessarily have to be closely
related.
The taxa regarded as seagrasses belong to a very
limited number of plant families, all classified within
the superorder Alismatiflorae (Monocotyledonae)
(Dahlgren et al., 1985), also generally known as
the Helobiae (Tomlinson, 1982). The subclass Alismatanae (Kubitzki, 1998) is with respect to its
contents identical with Alismatiflorae. Three out
of four families consist exclusively of seagrasses,
viz. the Zosteraceae, the Cymodoceaceae, and the
Posidoniaceae. In the past these families generally
have been classified as subfamilies of the Potamogetonaceae (Ascherson and Graebner, 1907; den
Hartog, 1970). Further studies have shown that
the latter family appeared to be too heterogeneous
(Tomlinson, 1982; Dahlgren et al., 1985), and had to
∗ Author for correspondence, email: c.denhartog@inter.nl.net
be split. So, apart from the Potamogetonaceae sensu
stricto, all of the former subfamilies were upgraded
to the family level. In fact some authors had already
long ago recognized the special identity of these
families, e.g. Dumortier who described the Zosteraceae as early as 1829 as an independent family
beside the Potamogetonaceae sensu stricto, and the
Zannichelliaceae. A fourth family, the Hydrocharitaceae, contains three genera that are considered
seagrasses, but the other 14 genera in this family are
confined to fresh-water habitats (Cook, 1990, 1998).
Apart from the families mentioned above which
have altogether 12 marine genera there are no other
genera that are fully confined to the marine environment. In other aquatic plant families so far only
two species have been found that occur exclusively in
marine habitats, viz. Ruppia aff. tuberosa of the family Ruppiaceae, and Lepilaena marina of the family Zannichelliaceae (Kuo and den Hartog, 2000).
The inclusion of these two species within the seagrasses is still a matter of debate. Descriptions of
these families and genera have been included in
the treatment of the monocotyledonous flowering
plants edited by Kubitzki (1998) (Hydrocharitaceae
by Cook; Ruppiaceae and Najadaceae by Haynes,
Holmberg-Nielsen and Les; Potamogetonaceae and
Zannichelliaceae by Haynes, Les and Holm-Nielsen;
Cymodoceaceae, Posidoniaceae and Zosteraceae by
Kuo and McComb). Furthermore, brief descriptions
of all presently described seagrass species, as well
as a key for the identification of them, have been
provided by Kuo and den Hartog (2001).
Arber (1920) formulated a set of four properties, which in her opinion were considered to be
c
1–23.
A. W. D. Larkum et al. (eds.), Seagrasses: Biology, Ecology and Conservation, pp.
2006 Springer. Printed in the Netherlands.