Review of the Trifolium amabile Complex in Peru, with the Description of a New Species

Here, we describe Trifolium absconditum sp. nov., a new species of the T. amabile complex from South America. It differs from other Peruvian Trifolia of the complex by having smaller stipules, leaves, inflorescences, and floral pieces. A key for Peruvian species of the complex is presented, and typifications for them are made when necessary and material is available in Peruvian herbaria. Thus, the number of Peruvian species in the complex is elevated to three: T. amabile, T. absconditum, and a resurrected T. peruvianum. Finally, it is suggested that Chile must be excluded from the distribution of this complex.


Introduction
Trifolium L. is a temperate and subtropical genus comprised of about 238 herbaceous species [1]. Within it, an American complex of around 20 species, found on dry mountain slopes from Mexico to Argentina, is currently considered as a single entity: Trifolium amabile Kunth, understood in a wide sense [2,3].
In Peru, the only recognized species of the Trifolium amabile complex is, indeed, T. amabile, a native caespitose herb; it is characterized with its nonrooting nodes, present in the introduced species of the genus occurring in the country, T. repens L. and T. polymorphum Poir. and for its conspicuously smaller leaflets than those of the also introduced T. hybridum L. [4,5]. It also differs from T. dubium and T. pratense, other introduced members of the genus, because they have a bigger habit.
Previously, another species was recognised: T. peruvianum; however, some researchers [5,6] put that name in synonymy with T. amabile, despite being a notably distinct plant and thus previously recognized [7,8]. Species of this complex are taxonomically located in subgenus Trifolium, section Involucrarium Hook ex Lojac., and may be, as a group, the origin of all the section of American clovers [9,10].
In the course of our investigations on Andean Peruvian rosids, we revised thoroughly the specimens deposited at Herbarium "Augusto Weberbauer" (MOL) in Lima, Peru, which referred to plants of the genus, and took special emphasis on the T. amabile complex species. Within it, the following species were recognized: T. amabile, T. peruvianum, and an unnamed species, characterized for its smaller habit evident in its narrower stipules, shorter leaflets, and smaller flowers. Despite the fact that T. amabile can be, in fact, highly variable, the consistency of the floral characters and their constant appearance at a definite range that did not overlap with those of the T. amabile sensu stricto nor with those of T. peruvianum, besides the occurrence at different altitudes of those species, convinced the author that a taxonomic difference could be established. A similar opinion is expressed in recent surveys on the genus [3] but without proposing nomenclatural acts [11]. Therefore, we are encouraged to publish ours, leaving non-Peruvian species out of the reach of this study. Here, we present the description of Trifolium absconditum sp. nov., along with descriptions of the other Peruvian species of this complex.
Additionally, a key for the Peruvian species of the complex is provided, all specimens consulted of the three involved taxa 2 Scientifica of the country are cited, and typifications of some taxa, when material is available in Peruvian herbaria, are made.

Materials and Methods
The specimens analysed are deposited in the cited herbaria. They were evaluated with a RadioShack digital-electronical caliper and studied under a Leica ZOOM 2000 stereoscope, and all the measures were repeated five times for each herbarium sheet. The characters evaluated are the ones used in the descriptions. Data were processed using Microsoft Excel. The photographs of specimens were taken with a Nikon D800E high-resolution camera. A survey to the Andean hills of Lima was made, in order to secure a complete specimen of Trifolium peruvianum.
The following Peruvian herbaria were consulted: "Augusto Weberbauer" (MOL), "San Marcos" (USM), and "Magdalena Pavlich" (HUPCH). Additionally, a photograph of a specimen from the Argentinian "Museo Botánico" (SI) was used, and the "Herbario Nacional" of Chile (SGO) was visited, in order to clarify the presence of this complex in the country.

Results
We present a key to determine the Peruvian species of the complex. Also, full descriptions are provided.

Key to the Species of the Trifolium amabile Complex in Peru
(1) Stipules longer than 6,8 mm. Leaflets longer than 6,5 mm.
Etymology. This species is so called since it has been commonly deposited in herbaria, but without being described all along. Geographical distribution is as follows: Peru and Argentina.
Notes. It can be easily recognized by its smaller overall aspect, with less and sparser flowers per inflorescence and the shorter stipules in mature leaves.

Discussion
Trifolium weberbaueri is rather problematic, since the description of the types refers to small plants (as the lectotype itself), which can fit in either T. absconditum or T. amabile if evaluated using vegetative characters [17]. However, the flower proportions (especially those of the wide banner petals) and the stipules' length of the isosyntype here lectotypified clearly set the species under synonymy with T. peruvianum, as recently suggested [2,3]. "Trifolium amabile var. pedicellaris Ball" is a commonly seen trinomial in Peruvian herbarium sheets; however, no bibliographic references were found for it. Anyway, the plants identified as such are consistently within our definition of T. peruvianum.
All species inhabit sandy soils; however, some specimens are cited for rocky or clay soils. The author had observed that species of this complex are also opportunistic, thriving in gardens and fodder pastures. In Peru, these plants are called "chullasapi, chullachaqui" (meaning "with one foot," referring to the long, deep, pivoted root; the former name is a corruption of the latter). It is used as a medication against lungs illness. The root is grinded, boiled, and then consumed; or it can be chewed raw (R. Castañeda, pers. comm.) Chile was included as a country where T. amabile do occur [14]. This seemed quite probable, although no other bibliographic reference or a specimen from there has been located. However, after a visit to the SGO, it became clear that no specimens of the complex are present; and thus, Chile should be excluded from the range of the complex until further notice.
Albeit the fact that discrete characters are recognized and we are sure morphometric approaches to the Trifolium amabile complex have been successful and appropriate, we strongly suggest molecular examinations of the validity of all taxa complex, including both Northern and Southern American species. Despite the works recently done by the cited American authors and the present work, increasing the quantity of recognized species of American trefoils while reducing the number of valid names, only genetic research will put beyond doubt all the valid species and therefore clarify definitively the taxonomy of this group.