Paspalum chilense Catanzaro & G.H. Rua, 2015

Catanzaro, María Paz, Bonasora, Marisa G., Speranza, Pablo R., Medina-Nicolas, Marcelo, Valls, José F. M. & Rua, Gabriel H., 2015, Paspalum chilense (Poaceae, Paspaleae): A new species from southern South America, Phytotaxa 197 (4), pp. 245-256 : 247-254

Paspalum chilense Catanzaro & G.H. Rua , sp. nov. ( Figs. 1 , 2A–C ).

Type:— CHILE. Región de los Ríos: provincia del Ranco, Lago Ranco, río Calcurrupe, 40º13’32.8”S, 72º14’22.4”W, 81 m, 18 December 2007, G. H. Rua, M. Medina-Nicolas & E. Piel 918 (Holotype (here designated) BAA, isotype CONC).

Paspalum nummularium simile , sed spiculis elongatioribus, breviteribus apiculatis et ligulis conspicue longioribus differt.

Cespitose perennials forming dense tufts. Tillers radiate spreading to ascending, their bases forming short slender rhizomes; culms 3–12 cm tall, ca. 0.9 mm diameter, 2–3-noded, unbranched, internodes compressed, glabrous. Leaves mostly crowded at the base. Leaf sheaths striate, keeled, glabrous, the lower short, overlapping. Ligule ca. 1.4 mm long, with a row of hairs ca. 0.3 mm long behind it. Blades flat, 2–4(–12) cm long, 2–4 mm wide, coarse pubescent on both surfaces; the blade of the uppermost leaf sharply reduced. Peduncles 2–6.5 cm long, glabrous. Inflorescence shortly exserted, composed of 2 subconjugate racemes, ascending to reflexed, 1.4–2.5 cm long; rachis ca. 0.8 mm wide. Spikelets 1.8–2 mm long, 1.4–1.5 mm wide, widely elliptical, apiculate at the apex; glume and sterile lemma subequal, firm, smooth and shiny, glume 5–nerved with the lateral nerves approximating the margins, lemma 3–nerved; upper floret ca. 1.7–1.9 mm long, widely elliptical, pale, minutely papillose, the palea slightly depressed, lodicules 2, ca. 0.3 mm long, truncate; stamens 3, anthers 0.6–0.8 mm long, purple; stigmas 2, deep purple. Caryopsis not seen.

Habitat and distribution: — Paspalum chilense is known from southern Chile, between ca. 36º and 41º S, in the regions VIII ‘Biobío’, IX ‘Araucanía’ (in both regions known only from ancient collections) and XIV ‘Los Ríos’ ( Fig. 3 ). The only recent collection was made in the vicinity of Lago Ranco (Region XIV), on the slopes of the Calcurrupe river valley, in meadow patches surrounded by woody areas ( Fig. 2 ) covered by a Nothofagus dombeyi – Eucryphia cordifolia forest, of the type known as ‘Bosque Laurifolio Templado Interior’ ( Luebert & Pliscoff 2006). This region has an average annual rainfall of 2500–4000 mm and an annual average temperature of 6–9ºC with 50 to 150 days of frost per year ( Moreno-González 2011).

Etymology: —The epithet refers to the Chilean endemic distribution of the new species.

Taxonomic observations: —The new species belongs to the Notata group sensu stricto (corresponding to the ‘core Notata’ group of Souza-Chies et al. 2006), which comprises perennial grasses with flat leaf blades at least 2 mm wide, racemes 2(3), conjugate or subconjugate, spikelets solitary, green to pale, ovate to suborbicular. Besides P. chilense , this group includes P. barretoi , P. bifidifolium , P. conduplicatum , P. minus , P. notatum , P. nummularium , P. pumilum , P. strigosum , and P. subciliatum (the latter two species were not sampled in the phylogenetic analysis).

The new species has been overlooked since specimens belonging to it had been cited elsewhere under P. pumilum ( Acevedo de Vargas 1947) or P. minus ( Zuloaga et al. 2004) . Nevertheless, P. chilense is a morphologically and cytologically distinct species. It is the only species in the group having ligules more than 1 mm long. Furthermore, spikelet shape and size ( Fig. 4 ) distinguish the new species from both P. pumilum (broadly ovate, apiculate vs. elliptical to ovate spikelets) and P. minus (spikelets up to 2 mm long vs. more than 2.2 mm long). Paspalum chilense is most similar to P. nummularium , from which it differs by having broadly ovate, apiculate (vs. orbicular, obtuse) spikelets and ligules 1.4 mm long (vs. 0.2–0.4 mm). On the other hand, the spikelets of the new species are very similar in shape to those of P. barretoi , but they do not exceed 2 mm in length (vs. 2.2–2.6 mm long in P. barretoi ). When length/width ratios were plotted against absolute length, the specimens of P. chilense were well discriminated from the other species of the core Notata group ( Fig. 5 ). The points representing specimens of P. chilense clustered together between P. nummularium and P. pumilum , the two species of the core Notata group with the smallest spikelets (although P. pumilum can also have longer spikelets).

Leaf anatomy: —Leaf blade expanded to open V-shaped in cross section. Midrib conspicuous, with abundant colorless parenchyma.Adaxial epidermis with bulliform cells and common epidermal cells scarcely differentiated.Abaxial epidermal cells with inflated external walls. Cuticles thin. Stomata present in both epidermal surfaces. Mesophyll composed of radial chlorenchymatous cells. Three orders of vascular bundles present, but bundles of second and third order obscurely differentiated, all vascular bundles surrounded by a single bundle sheath of parenchymatous cells; the bundles separated by 2–3 parenchyma cells. Abaxial and adaxial sclerenchyma caps associated with first and second order vascular bundles ( Fig. 6 ).

Cytology: —Chromosome counting of the typus material revealed that P. chilense is a diploid species with 2n =20 chromosomes. Meiotic behavior is normal, with formation of 10 bivalents ( Fig. 7 ). Paspalum chilense , here newly recognized as a distinct species, and P. barretoi , currently included in the synonymy of P. minus ( Zuloaga & Morrone 2003, 2005, Zuloaga et al. 2004), have been considered conspecific with P. minus , an apomictic pentaploid widely distributed in tropical America from Mexico and Cuba to Paraguay ( Davidse & Pohl 1978, Honfi et al. 1990, Bonilla & Quarín 1997, Honfi 2003). Other ploidy levels have been reported for P. minus ; however, the diploid cytotypes of P. minus reported by Banks (1966) correspond to P. pumilum , based on observations of the specimens Banks 3395 and Banks 3500 at MO (images available at http://tropicos.org/Name/25509844). The identities of the tetraploids reported by Gould (1958) and Davidse & Pohl (1978) under P. pumilum could not be confirmed. The specimen Gould 7568 has not been available to us, whereas the specimen Davidse 5378 (MO, image available at http://tropicos.org/Image/100283298) corresponds to P. minus . In addition, the reported chromosome count for Davidse 5378 was imprecise (n =ca. 20) so a pentaploid (2n =5x=50) complement cannot be confidently ruled out for this individual. Consequently, besides morphological differentiation, specimens of the closely related P. chilense and P. barretoi , which inhabit relatively high and cold areas in southern Chile and southern Brazil respectively, exclusively comprise sexual diploids (2n =20), a chromosome number not reported with certainty for P. minus .

IUCN Red List category: —Recent collections of this species are only known from Lago Ranco, Chile. Two specimens conserved in the herbarium M document the occurrence of the species in a much broader area in the last decade of the XIX century, suggesting that the extent of occurrence of the species has been reduced or that it simply has not been re-collected there. In view of this, we consider this a rare and/or inconspicuous species. Paspalum chilense should be considered in the category of Endangered (EN) according to IUCN Red List criteria ( IUCN 2001), because of its restricted geographical distribution. Further field data are necessary to confirm this conservation status.

Since conservation policies are mostly based on species lists, species usually constitute the unit to be conserved. However, the application of the term ‘species’ to a group of organisms can be considered in dramatically different ways depending on the species concept applied ( Agapow et al. 2004 and references therein). Cytologically, ecologically, or reproductively differentiated populations that are not easily diagnosable in herbarium specimens, may go unnoticed to conservation policy makers. This seems to be the case of P. chilense and P. barretoi , two species that are threatened due to the limited size and high specificity of their geographical ranges. Indeed, the identity of both diploid species has been obscured under the synonymy of P. minus , and therefore they remained overlooked as threatened taxa.

Phylogenetic relationships: —In the parsimony analysis, two most parsimonious trees were found (17 steps, CI=0.85, RI=0.65). Paspalum chilense , P. minus , P. pumilum , P. nummularium , and P. barretoi group together into a well-supported clade, sister to P. notatum . Phylogenetic relationships within this clade were poorly resolved ( Fig. 8 ).

Biogeography: —The discovery of P. chilense in southern Chile has interesting biogeographical implications since it provides additional evidence for the relationships between the floras of southern Chile and southern Brazil. Indeed, many floristic elements are shared between both regions, particularly concerning the peat soil area along the humid southeastern edges of the Brazilian ‘Planalto meridional’, in the states of Santa Catarina and Rio Grande do Sul. This region is inhabited by several plant genera clearly related to the Austral–Antarctic flora, such as Araucaria, Drymis, Escallonia, Podocarpus, Gunnera, Acaena, Fuchsia, Griselinia ( Rambo 1953), and Alstroemeria ( Aagesen & Sanso 2003) . It has been postulated ( Villagrán & Hinojosa 1997) that there was a geographical continuity of forests across subtropical South America until the Miocene, which would explain the floristic relationships between southern Chilean and southern Brazilian forests. This extensive forest area would have been fragmented as a consequence of the formation of a South American ‘Arid Diagonal’ during the Pliocene. Interestingly, the only other species of Paspalum occurring in southern Chile, the sexual tetraploid P. dasypleurum Kunze ex Desvaux (1854: 242) , also has a closely related counterpart in the Brazilian Southern Planalto: the also sexual tetraploid P. dilatatum biotype ‘Vacaria’, which may deserve species status ( Speranza 2009). Moreover, both the Notata and Dilatata groups include cold-tolerant species from temperate southern regions, and show disjunct distribution patterns with greater diversity in eastern areas and some isolated representatives in the west.

Additional specimens examined:— CHILE. Región de la Araucanía: provincia de Cautín, Villarrica, 1897, F.W. Neger s.n. (M). Región del Biobío: provincia Concepción, Concepción, 1893–96, F.W. Neger s.n. (M). Región de los Ríos: provincia del Ranco, Lago Ranco, río Calcurrupe, 19 December 1944, O. Boelcke 324 (BAA, SI).

Key to the species of Paspalum , core Notata group

1. Spikelets (2.8–) 3–4 mm long; plants creeping .................................................................................................................. P. notatum

- Spikelets up to 2.8 mm long; plants cespitose .................................................................................................................................. 2

2. Spikelets pilose, at least on the upper glume .................................................................................................................................... 3

- Spikelets glabrous ............................................................................................................................................................................. 4

3. Spikelets 2.4–2.7 mm long, ovate ............................................................................................................................... P. subciliatum

- Spikelets ca. 2 mm long, broadly ovate ........................................................................................................................... P. strigosum

4. Proximal leaf sheaths keeled, conduplicate; spikelets ca. 2 mm wide ..................................................................... P. conduplicatum

- Proximal leaf sheaths not keeled, convolute; spikelets usually up to 1.9 mm wide (occasionally up to 2 mm in P. barretoi ).........5

5. Spikelets more than 2.2 mm long and 1.5 mm width........................................................................................................................6

- Spikelets generally up to 2.1 mm long, width 1–1.7 mm (up to 2.4 mm long in P. pumilum , but then less than 1.5 mm width) ... 7

6. Racemes ascending at maturity, conjugate to approximate, the internode between them rarely reaching 5 mm long; spikelets acute ....................................................................................................................................................................................... P. minus

- Racemes reflexed at maturity, subconjugate, separated by an internode more than 5 mm long; spikelets shortly apiculate ............. ............................................................................................................................................................................................. P. barretoi

7. Spikelets elliptical to ovate, length/width ratio greater than or equal to 1.4. ................................................................................... 8

- Spikelets broadly ovate to orbicular, length/width ratio up to 1.4..................................................................................................... 9

8. Leaf blades conspicuously bifid at apex ...................................................................................................................... P. bifidifolium

- Leaf blades not bifid at apex ............................................................................................................................................ P. pumilum

9. Spikelets obtuse, length/width ratio up to 1.2; ligule 0.2–0.4 mm long.................................................................... P. nummularium

9. Spikelets apiculate, length/width ratio greater than 1.2; ligule ca. 1.4 mm long. .............................................................. P. chilense

Figures

FIGURE 1. Paspalum chilense sp. nov.A. Habit. B: Detail of ligule. C. Spikelet, abaxial view. D. Spikelet, adaxial view. E. Upper floret, adaxial view. F. Upper floret, abaxial view. G. Upper floret, palea and lodicules. Drawn from the type specimen (Rua et al. 918) by Natalia Gómiz.

FIGURE 2. Paspalum chilense sp.nov.Field photographs from the type collection.A.Plant,showing the cespitose habit.B. Inflorescences, each composed of two subconjugate, divergent racemes. C. Detail of spikelets at anthesis. D. Habitat, in the vicinity of Lago Ranco, Chile. Photographs by G. H. Rua.

FIGURE 3. Distribution of Paspalum chilense sp. nov. and the related species P. barretoi, P. pumilum, P nummularium, P. conduplicatum, and P. minus. The new species occurs near the southern limit of the generic distribution.

FIGURE 4. Comparative view of spikelets of A. Paspalum chilense sp. nov. (Rua et al. 918). B. P. barretoi (Rua et al. 736). C. P. minus (Valls 15229). D. P. nummularium (Rua et al. 737). E. P. pumilum (Parodi 163).

FIGURE 5. Spikelet length/width ratio vs. spikelet length plot showing differences in shape and size between P. chilense sp. nov. and the related species P. nummularium, P. barretoi, P. pumilum, P. minus, and P. conduplicatum.

FIGURE 6. Paspalum chilense sp. nov. Transverse section of the leaf blade (from the type collection).

FIGURE 7. Meiotic microsporocyte of Paspalum chilense sp. nov. (Rua et al. 918) at diakinesis showing 10II.

FIGURE 8. Phylogenetic relationships of P. chilense sp. nov. and related species in the Notata group s.s., obtained from four cp-DNA markers. Strict consensus of two most parsimonious trees (length=17). Numbers above branches indicate Bremer support, those below branches represent symmetric jackknifing frequencies. Chromosome numbers are indicated beside each species name.