193
7.2.1 An Ancient Species with a Huge Natural
Distribution Area
Salix humboldtiana Willd. (Spanish names, sauce nativo, sauce amargo, sauce
colorado, sauce criollo; original people names, reiwe, waik, yvira puku, wayaw),
the only willow tree native to Argentina, is one of the tree species with the longest
natural distribution area in the world. It spreads over more than 10,000 km covering
an enormous latitudinal gradient from Central-North Mexico (23°N) to Chubut
River (44°S), in the Argentine Patagonia. Consequently, it grows in a great diversity
of environmental conditions, as riparian vegetation (Hauman et al. 1947; Ragonese
and Rial Alberti 1958a). It occurs mostly along the Andes Mountains and adjacent
regions, following watercourses in subhumid and semi-arid regions, from the sea
level up to more than 3900 m asl (Flora Argentina 2014; IUCN 2020). In the subtropical and tropical climates, it is found essentially in the Yungas, in some Andean
Valleys and along the Amazon River and its tributaries, in the periphery of the
Amazonia towards the Andes. In Argentina, it is widely distributed, being present in
almost the whole country, except for the high altitudes of the Andes and South
Patagonia (Fig. 7.8).
Salix humboldtiana is a medium-size tree, growing up to 25 m in height and up
to 1 m in diameter. It is a pioneer species (Parolin et al. 2002; Isebrands and
Richardson 2014) and can tolerate long periods of flooding, with reports of up to 7
months with submerged roots (Parolin et al. 2002). However, it is frost sensitive,
which leads to some range restrictions in the cold environments like those of high
altitudes and the South Patagonian steppe.
With 20 to 25 million years of evolution, it is an ancient and phylogenetically
basal species of the genus and probably the origin of many other Salix species
(Abdollahzadeh et al. 2011; Wu et al. 2015). While most of the willows are polyploids (Abdollahzadeh et al. 2011; Lauron-Moreau et al. 2015; Wu et al. 2015,
2018), S. humboldtiana is a diploid. Its evolutionary origin occurred in the subtropical New World and from there migrated to the southern part of South America
adapting to low temperatures (Argus 1997).
It regenerates mainly through seeds dispersed by wind or water and commonly
builds sapling stands on sand or lime banks (Thomas and Leyer 2014). It has very
narrow leaves (0.6–0.8 mm), not so long (6–13 cm), some of them slightly curved
and sawed (Ragonese and Rial Alberti 1958a; Menendez 2012; Fig. 7.9). It is a
perennial species when it occurs in warm tropical and subtropical climate conditions, but deciduous in climates with a definite cold or dry season. Male flowers
have between five and eight stamens, which is also a discriminating trait in relation
to most other willows, which normally have two stamens. Pollination, like in other
willow species, has two vectors: insects and wind (Tamura and Kudo 2000).
The main adult trunk has a rough bark with irregular plates, and its architecture
is very characteristic and quite different from that of the exotic feral willows abundant in the same ranges, since it has a very straight, monopodial (or
7 Araucaria araucana and Salix humboldtiana…
7.2.1 An Ancient Species with a Huge Natural
Distribution Area
Salix humboldtiana Willd. (Spanish names, sauce nativo, sauce amargo, sauce
colorado, sauce criollo; original people names, reiwe, waik, yvira puku, wayaw),
the only willow tree native to Argentina, is one of the tree species with the longest
natural distribution area in the world. It spreads over more than 10,000 km covering
an enormous latitudinal gradient from Central-North Mexico (23°N) to Chubut
River (44°S), in the Argentine Patagonia. Consequently, it grows in a great diversity
of environmental conditions, as riparian vegetation (Hauman et al. 1947; Ragonese
and Rial Alberti 1958a). It occurs mostly along the Andes Mountains and adjacent
regions, following watercourses in subhumid and semi-arid regions, from the sea
level up to more than 3900 m asl (Flora Argentina 2014; IUCN 2020). In the subtropical and tropical climates, it is found essentially in the Yungas, in some Andean
Valleys and along the Amazon River and its tributaries, in the periphery of the
Amazonia towards the Andes. In Argentina, it is widely distributed, being present in
almost the whole country, except for the high altitudes of the Andes and South
Patagonia (Fig. 7.8).
Salix humboldtiana is a medium-size tree, growing up to 25 m in height and up
to 1 m in diameter. It is a pioneer species (Parolin et al. 2002; Isebrands and
Richardson 2014) and can tolerate long periods of flooding, with reports of up to 7
months with submerged roots (Parolin et al. 2002). However, it is frost sensitive,
which leads to some range restrictions in the cold environments like those of high
altitudes and the South Patagonian steppe.
With 20 to 25 million years of evolution, it is an ancient and phylogenetically
basal species of the genus and probably the origin of many other Salix species
(Abdollahzadeh et al. 2011; Wu et al. 2015). While most of the willows are polyploids (Abdollahzadeh et al. 2011; Lauron-Moreau et al. 2015; Wu et al. 2015,
2018), S. humboldtiana is a diploid. Its evolutionary origin occurred in the subtropical New World and from there migrated to the southern part of South America
adapting to low temperatures (Argus 1997).
It regenerates mainly through seeds dispersed by wind or water and commonly
builds sapling stands on sand or lime banks (Thomas and Leyer 2014). It has very
narrow leaves (0.6–0.8 mm), not so long (6–13 cm), some of them slightly curved
and sawed (Ragonese and Rial Alberti 1958a; Menendez 2012; Fig. 7.9). It is a
perennial species when it occurs in warm tropical and subtropical climate conditions, but deciduous in climates with a definite cold or dry season. Male flowers
have between five and eight stamens, which is also a discriminating trait in relation
to most other willows, which normally have two stamens. Pollination, like in other
willow species, has two vectors: insects and wind (Tamura and Kudo 2000).
The main adult trunk has a rough bark with irregular plates, and its architecture
is very characteristic and quite different from that of the exotic feral willows abundant in the same ranges, since it has a very straight, monopodial (or
7 Araucaria araucana and Salix humboldtiana…