et al. 2011), have been highlighted in several recent studies. For example, Pyšek
et al. (2013) noted that 20% of alien plant species listed in South Africa’s Conservation of Agricultural Resources Act had no herbarium records in the country’s
National Herbarium. There have been efforts to improve the accuracy of inventories
of alien plant taxa, and several detailed studies have been undertaken recently to
confirm the identity of taxa in groups with poorly resolved taxonomic status and for
other important plant groups.
Magona et al. (2018) conducted a comprehensive assessment of the presence of
Australian Acacia species (wattles) in South Africa. Using herbarium records, visits
to known planting sites, field surveys, and molecular methods, they concluded that
although records exists for introductions of 141 species to South Africa, only
33 species are definitely still present, 13 of which are invasive. Importantly, several
of the invasive species are not on Glen’s list, and many species on Glen’s list could
not be found at known planting sites. Walters et al. (2011) estimated that around
400 alien species of Cactaceae are present in South Africa, and Novoa et al. (2017)
presented evidence that about 300 species of cacti are imported to South Africa
annually (though the vast majority of these are not new to South Africa). Currently,
35 species of Cactaceae are invasive (Kaplan et al. 2017). Milton (2004) produced a
preliminary list of 113 alien grass species present in South Africa. Visser et al.
(2017) updated this inventory, using recorded occurrences from many literature and
database sources. They concluded that at least 256 alien grass species are present,
37 of which are invasive. One clade of grasses (subfamily Bambusoideae; ‘bamboos’) was examined in more detail by Canavan et al. (2019), who found evidence
for the presence of 34 currently recognised alien bamboo taxa in South Africa.
Jacobs et al. (2017) reviewed evidence for the presence of Melaleuca species
(Paperbark Trees; including taxa formerly included in the genus Callistemon) in
South Africa. They concluded that at least 36 species are currently present in the
country. Le Roux et al. (2010) used molecular methods to confirm the presence of
Anigozanthos flavidus (Evergreen Kangaroo Paw), which had been tentatively
identified based on morphological features; they also identified a second naturalised
species, A. rufus (Red Kangaroo Paw), not previously recorded from South Africa.
Taxa within several alien plant genera (e.g. Eucalyptus, Oenothera, Opuntia, Pinus,
Prosopis, Rubus, Salix and Senna) are only identified to the genus level in some lists
and mapping exercises, and in some cases questionable species identifications
are made.
These examples show that, even for very conspicuous and well-studied plant
species from taxonomically well-resolved groups (e.g. wattles), further work is
needed to confirm the identity and introduction status of alien taxa. The situation
is worse for taxa that are less well studied, less conspicuous, or difficult to identify.
This has important implications for understanding aspects of the invasion ecology of
species (e.g. matching plant species to host-specific bacterial and mycorrhizal
symbionts to evaluate the role of mutualisms) and for management (e.g. when
considering biological control).
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D. M. Richardson et al.
et al. (2013) noted that 20% of alien plant species listed in South Africa’s Conservation of Agricultural Resources Act had no herbarium records in the country’s
National Herbarium. There have been efforts to improve the accuracy of inventories
of alien plant taxa, and several detailed studies have been undertaken recently to
confirm the identity of taxa in groups with poorly resolved taxonomic status and for
other important plant groups.
Magona et al. (2018) conducted a comprehensive assessment of the presence of
Australian Acacia species (wattles) in South Africa. Using herbarium records, visits
to known planting sites, field surveys, and molecular methods, they concluded that
although records exists for introductions of 141 species to South Africa, only
33 species are definitely still present, 13 of which are invasive. Importantly, several
of the invasive species are not on Glen’s list, and many species on Glen’s list could
not be found at known planting sites. Walters et al. (2011) estimated that around
400 alien species of Cactaceae are present in South Africa, and Novoa et al. (2017)
presented evidence that about 300 species of cacti are imported to South Africa
annually (though the vast majority of these are not new to South Africa). Currently,
35 species of Cactaceae are invasive (Kaplan et al. 2017). Milton (2004) produced a
preliminary list of 113 alien grass species present in South Africa. Visser et al.
(2017) updated this inventory, using recorded occurrences from many literature and
database sources. They concluded that at least 256 alien grass species are present,
37 of which are invasive. One clade of grasses (subfamily Bambusoideae; ‘bamboos’) was examined in more detail by Canavan et al. (2019), who found evidence
for the presence of 34 currently recognised alien bamboo taxa in South Africa.
Jacobs et al. (2017) reviewed evidence for the presence of Melaleuca species
(Paperbark Trees; including taxa formerly included in the genus Callistemon) in
South Africa. They concluded that at least 36 species are currently present in the
country. Le Roux et al. (2010) used molecular methods to confirm the presence of
Anigozanthos flavidus (Evergreen Kangaroo Paw), which had been tentatively
identified based on morphological features; they also identified a second naturalised
species, A. rufus (Red Kangaroo Paw), not previously recorded from South Africa.
Taxa within several alien plant genera (e.g. Eucalyptus, Oenothera, Opuntia, Pinus,
Prosopis, Rubus, Salix and Senna) are only identified to the genus level in some lists
and mapping exercises, and in some cases questionable species identifications
are made.
These examples show that, even for very conspicuous and well-studied plant
species from taxonomically well-resolved groups (e.g. wattles), further work is
needed to confirm the identity and introduction status of alien taxa. The situation
is worse for taxa that are less well studied, less conspicuous, or difficult to identify.
This has important implications for understanding aspects of the invasion ecology of
species (e.g. matching plant species to host-specific bacterial and mycorrhizal
symbionts to evaluate the role of mutualisms) and for management (e.g. when
considering biological control).
74
D. M. Richardson et al.