Patagonian Vegetation - Terrestrial Biozones

Patagonian Vegetation - Terrestrial Biozones

Plant Formations in the Patagonian BioProvince
Peter Martin Rhind
Patagonian Occidental Semi-Desert and Steppe
This zone extends in a strip 100-120 km wide from Neuge’n Province to the northwest
corner of Santa Cruze. The dominant plants are tussock grasses, with Stipa species such
as S. humilis and S. speciosa, well represented. Other grasses include Bromus setifolius,
Hordeum comosum, Poa lanuginosa and the endemic or near endemic Festuca argentina
(Poaceae). However, the colour of this formation is rarely green being usually
characterized by tones of yellow, grays and brown. In fact, a large proportion of the flora
has yellow flowers. The most common shrubs are Adesmia campestris, Senecio
filaginoides and the near endemic Mulinum spinosum (Apiaceae), but the tallest shrubs
are Berberis cuneata and B. heterophylla. These latter species are also distinguished by
their deep green colour. Other common shrubs include Lycium chilense, Nardophyllum
obtusifolium, Schinus polygamus, Verbena ligustrina and the endemic Acantholippia
seriphioides (Verbenaceae). Occasionally in the central part of this zone the endemic or
near endemic Sapium patagonicum (Euphorbiaceae) predominates. It is a strange leafless
plant with branches emerging from the centre of the plant, and is also poisonous. There
are also several cacti such as the endemic Maihuenia patagonica (Cactaceae) and here
represent the southernmost members of the family. The field layer includes a rich
assemblage of herbaceous species. These typically include sedges such as the Carex
andina and the endemic Carex argentina (Cyperaceae) and a variety of forbs. Among the
endemic or near endemic are Arjona patagonica (Santalaceae), Gilia patagonica
(Polemoniaceae), Loasa argentina (Loasaceae), Plantago patagonica (Plantaginaceae)
and Polygala darwiniana (Polygalaceae). However, these semi-deserts show considerable
variations in terms of both composition and physiognomy. In certain valleys, for example,
there are saline soils subject to occasional flooding. Here the conspicuous taxa include
Puccinellia skottsbergii, species of Distichlis, and the endemic or near endemic Lycium
repens (Solanaceae), Nitrophila australis (Amaranthaceae) and Suaeda patagonica
(Chenopodaceae).
Patagonian (Chubutian) Semi-Desert and Steppe
This zone includes much of Chubut extending south from the Rio Negra to a broad
transitional zone around the border with Santa Cruz. On the plains, plateaus and hills the
vegetation is dominated by the grasses Poa ligularis, Stipa humilis and S. speciosa
together with the endemic composites Chuquiraga avellandae, Nassauvia glomerulosa
and N. ulicina (Asteraceae) although much of it is very sparse. Chuquiraga is a shrub with
spiny leaves and can reach heights of about 60 cm, while Nassauria species are dwarf
cushion plants. Nassauvia glomerulosa often mimics the shape and colour of pebbles.
Another characteristic species include the endemic Pleurophora patagonia (Lythraceae).
This attractive plant is often covered in pink flowers during summer. Where saline
conditions prevail, halophytes such as the endemic Atriplex lampa, A. sagittifolia
(Chenopodiaceae) and Frankenia patagonica (Frankeniaceae) predominate. However,
these areas tend to be sparsely vegetated and represent some of the most desert-like
landscapes in Patagonia. So-called badlands can also be found around the Sarmiento
Basin. Here endemic species such as Ameghinoa patagonica (Asteraceae) and Nicotiana
ameghinoi (Solanaceae) occur.
Patagonian (Santacruzian) Semi-Desert and Steppe
This arid formation extends from 46 to 51 degrees south from the coast to the Andes. It
has strong affinities with the Chubutian zone but lacks Chuquiraga avellanedae. Here it is
Copyright © 2010 Peter Martin Rhind
replaced by Verbena tridens as one of the main dominants, which can grow to a height of
about 100 cm. The principal vegetation is shrub steppe in which species such as
Brachyclados caespitosus, Mulinum microphyllum and the endemic Acantholippa
seriphioides (Verbenaceae) and Chuquiraga aurea (Asteraceae) are characteristic.
Bunchgrass including Stipa humilis, S. speciosa and S. chrysophylla is also common
together with the feathered spiked grasses like Stipa neaei, S. psylantha and S.
subplumosa. In hilly areas Acanthophyllum rigidum, Berberis heterophylla, Lycium
chilense, Nardophyllum obtusifolium, Schinus polygamus and Verbena ligustrina become
more frequent but none of them dominate.
Patagonian (San Jorge Gulf) Semi-Desert and Steppe
This zone forms a narrow arc bordering the Gulf of San Jorge stretching from Cabo Raso
to Punta Casamayor, and comprises plateaus and many narrow valleys. Much of the
vegetation consists of dense scrub dominated by Colliguaya integerrima and the endemic
or near endemic Trevoa patagonica (Rhamnaceae). Other shrubs include Adesmia
campestris, Anarthrophyllum rigidum and the endemic Ephedra ochreata (Ephedraceae).
Ephedra is the only genus of gymnosperm in Patagonia and can be an important
component of the vegetation in places. Beneath the open canopy the herbaceous field
layer is usually dominated by grass in which species of Stipa are important but the annual
grass Vulpia dertonensis may also form extensive patches in spring. Other herbaceous
species include Amsinckia hispida, Calceolaria lanceolata, Huanaca acaulis, Microsteris
gracilis, Oenothera contorta, Plagiobotris calandrinioides and Silene magellanica. A
number of climbing species may also be present including the endemic Loasa argentina
(Loasaceae), Magallana porifolia (Tropaeolaceae) and Mutisia retrorsa (Asteraceae). At
high elevations on the Del Castillo Plateau the vegetation changes. Here grasses such as
Festuca argentina, F. pallescens and Poa ligularis mainly dominate. However, the winds
here are stronger than anywhere else in Patagonia and this no doubt acts as a limiting
factor for many species. Shrubs therefore are few in number, but cushion plants are well
represented. Typical amongst these are Brachyclados caespitosus, Cruckshanksia
glacialis and the endemic or near endemic Benthamiella patagonica (Solanaceae). These
high plateaus also provide habitat for the endemic Larrea ameghinoi (Zygophyllaceae),
which is the southernmost limit of the genus. It is also the only species in the genus that
has a carpet-like habit.
Further information required.
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Copyright © 2010 Peter Martin Rhind