Xylopodia laurensis C.M. Martin & C.A. Zanotti, 2022

Martin, Claudia M., Zanotti, Christian A., Acuna-Castillo, Rafael, Henning, Tilo, Catari, Juan C. & Weigend, Maximilian, 2022, Taxonomic revision of the peculiar genus Xylopodia (Loasaceae) with a new species from Argentina and Bolivia demonstrating an atypical trans-Andean disjunction, PhytoKeys 194, pp. 47-62 : 47

Xylopodia laurensis C.M. Martin & C.A. Zanotti sp. nov.

Fig. 3

Diagnosis.

Xylopodia laurensis is closely related to Xylopodia klaprothioides Weigend, but the former is readily distinguishable by the sepals reflexed in anthesis, petals greenish white with a long claw (ca. 1/3 of petal length); back of nectar scale white, apically striped green and yellowish; free staminodes are dimorphic, ligulate, the central pair with a conspicuous, papillose, scale-like filament flange below the middle.

Type.

Argentina: Prov. Jujuy, Dpto . San Pedro, San Juan de Dios, Estancia Las Lauras, camino al “Chorro”, a tres metros del arroyo Chico , 24°33'49.8"S, 64°39'05.8"W, 925 m, 22 Aug 2021, C. M. Martín 2887 (holotype SI)

Description.

Shrub with erect shoots up to 130 cm tall from a short horizontal xylopodium (= ligneous rhizome), ca. 5 × 3 cm, sometimes divided into 3-4 branches distally; aerial vegetative organs densely hairy, with white scabrid and glochidiate trichomes, ca. 0.5 mm long. Leaves opposite, 14-22 × 13-9 cm, lamina with 1-2 lobes in each side, margin serrate, apices acute to rounded, base cuneate, petiole 1.5-3 cm long. Inflorescences terminal dichasia; peduncle ca. 6 cm long; basal bracts 3 × 2 cm, 3-lobed, margin denticulate, base cuneate; distal bracts 0.8-1.8 × 0.3-0.5 cm, lanceolate, margin entire. Flowers tetramerous, pedicels 4-6 mm long, deflexed. Sepals broadly triangular, ca. 5 × 3 mm, margins entire, erect in bud, reflexed during anthesis, and pubescent on both sides, pubescence similar to that of vegetative organ. Petals 7 × 3 mm, greenish white, unguiculate, with a long claw (ca. 1/3 of petal length), cucullate in the distal half, with two membranous longitudinal lamellae with densely ciliate margin, aestivation valvate, margin with a tooth on each side near the middle, where the limb starts, dorsal veins three, with scabrid-glochidiate trichomes abaxially, mostly glabrous adaxially. Nectar scales 4, antesepalous, 4 × 3 mm, cucullate, formed apparently by 6 fused staminodes, mostly white, pubescent in lower half, striped green and yellowish in distal third, apex green, slightly recurved. Free staminodes 4 per scale, opposite and internal to it, dimorphic, their lower halves partly fused, densely pubescent, with laciniate margins, central staminodes green, 4 mm long, with a conspicuous, papillose, scale-like filament flange below the middle, apex reflexed, spathulate the lateral ones yellowish-white, 5.3 mm long, with a filiform apex. Fertile stamens arranged in 4 antepetalous groups of ca. 7 per petal, free, filament ca. 6 mm long, base pubescent, anthers white, with two obovate thecae. Ovary half-superior, broadly ovate to conical; style to 5 mm long, lower half pubescent, stigma with four ribs tapering towards the apex. Fruits subglobose capsules, with a conical, slightly asymmetrical apex, opening with 4 apical valves.

Etymology.

The name of the species refers to the locality of the type collection in Argentina (Estancia Las Lauras, Jujuy, Argentina).

Distribution.

Xylopodia laurensis grows on the eastern slope of the Andes from Bolivia (Dptos. La Paz and Chuquisaca) to northern Argentina (Prov. Jujuy) at elevations from 850-900 m asl (Jujuy and Chuquisaca) to 2360 m asl (La Paz) (Fig. 1 ). The known distribution thereby covers a latitudinal range of ca. 1000 km in a straight line between the northernmost locality in Dpto. La Paz and the southernmost population from Prov. Jujuy. The distributional range is even larger (~1300 km) when following the curve of the eastern slope of the Andes along a suitable elevation with appropriate climatic conditions and respective available habitats. X. laurensis can hence be considered a rather widespread taxon, albeit with very specific saxicolous habitat requirements, and this contrasts markedly with the very narrow endemism of its sister taxon, X. klaprothioides . Narrow endemism as found in X. klaprothioides is a common pattern reported for many plant groups whose elements reach into the Amotape-Huancabamba zone (e.g. Gentianaceae - Struwe et al. 2009; Boraginaceae - Weigend et al. 2010; Grossulariaceae , Urticaceae - Mutke et al. 2014; Solanaceae - Deanna et al. 2018; Arecaceae - Escobar et al. 2018; Lentibulariaceae - Casper et al. 2020; Henning et al. 2021) and particularly common in the Loasaceae ( Henning and Weigend 2009; Henning et al. 2011, 2019; Mutke et al. 2014).

Ecology.

Xylopodia laurensis occurs in the understory of seasonally dry (scrub) forest in shallow rocky soil and in soil pockets on rock-outcrops across its range (Fig. 4 ). In Argentina, it grows in xerophilous and deciduous forests (Fig. 4A ) at 925 m a. s. l. corresponding to the Chaco Occidental phytogeographic district sensu Cabrera 1994. Typical components are Schinopsis lorentzii (Griseb.) Engl., Libidibia paraguariensis (D. Parodi) G.P. Lewis, Handroanthus impetiginosus (Mart. ex DC.) Mattos, Ceiba chodatii (Hassl.) Ravenna, Aspidosperma quebracho-blanco Schltdl. and Athyana weinmanniifolia (Griseb.) Radlk. In Chuquisaca, Xylopodia laurensis forms small colonies on rocky outcrops and the margins of temporary streams (torrenteras, Fig. 4B ) in the Boliviano-Tucumano Seasonal Dry Forests (Pilcomayo-Alto Parapeti Sector of the Boliviano-Tucumano Biogeographic Province sensu Navarro and Maldonado 2002 and Navarro and Ferreira 2009). The most common species here are Schinopsis lorentzii , Anadenanthera colubrina (Vell.) Brenan, Ceiba chodatii , Saccellium lanceolatum Bonpl., Piptadenia boliviana Benth., Ruprechtia apetala Wedd. and Libidibia paraguariensis . These rock outcrop habitats are poorly studied in Bolivia and several new species from other plant groups still await description (JC unpublished data). In La Paz, the new species is found in the Yungueño Montane semi-deciduous forest. This area has been more profoundly influenced by human activities. The original forests have been replaced by scrub and secondary forests (these correspond to the Cuenca Alta del Beni Sector of the Yungueña Peruviana-Boliviana Biogeographic Province sensu Navarro and Maldonado 2002 and Navarro and Ferreira 2009).

Phenology.

The flowering and fruiting of this species have been recorded in the dry season, from late August to mid-September in Jujuy and from April to August in Chuquisaca. In Chuquisaca, plants lose their foliage by August and produce new leaves when the rainy season starts in October to November.

Additional specimens examined.

Bolivia: Dpto. Chuquisaca. Prov. Luis Calvo, Municipio Villa Vaca Guzmán, A 5.5 km al Norte de la Comunidad Ivoca y 3 km al Este de la Quebrada Angoba. Estancia del Sr. Jhony Labras. 850 m, 11. Sep. 2019, J.C. Catari & Z. Pérez 2501 (USZ); same locality, 17. Oct. 2021, J.C. Catari 2510 (USZ). Photographs examined : Bolivia: Dpto. La Paz, Prov. Larecaja, Municipio Sorata, Cueva de San Pedro, s.d., autor: A.F. Fuentes (available in http://legacy.tropicos.org/Image/100494035)

Notes.

Xylopodia laurensis is a close ally of Xylopodia klaprothioides . Vegetatively, it mainly differs in the much smaller woody rhizome, which easily reaches 30 cm and more in length in mature X. klaprothioides . Aerial stem and leaf morphology appear to be similar, although the leaves of X. klaprothioides are usually smaller and not as deeply lobed (Figs 2F , 3F ). The major differences, however, are found in the details of floral morphology, where X. laurensis differs in its reflexed (versus spreading) sepals during anthesis (Figs 2A-B , 3A-B ), floral scale coloration (white and yellowish-green pattern apically versus uniformly green with yellowish scale neck, Figs 2A-B, D , 3A-B, E ) and the morphology of the staminodes (Figs 2E , 3D ). The central staminodes are particularly distinctive and their enlarged filament flanges resemble those of Kissenia capensis R.Br. ex Harv. ( Urban and Gilg 1900).

There is a disjunction of ca. 1500 km between the populations of X. klaprothioides in northern Peru and X. laurensis in Bolivia (Fig. 1 ). The recent discovery of this genus demonstrates that it is very difficult to locate in the field - mostly because it has few if any leaves when in flower, and the green flowers are hardly differentiated from the surrounding vegetation, rendering visual recognition of even flowering plants a genuine challenge. If found when sterile, it could be confused with some other oppositely leaved subshrubs or shrubs (high magnification lenses are necessary to see the distinctive scabrid-glochidiate trichomes, Fig. 5 ). Likewise, the species, even if widely distributed, could be very localized in distribution. One of us (JC) explored an area of ca. 10 ha of suitable habitat near the collection locality in Chuquisaca and was able to locate only two small colonies distributed in an area of <1000 m2. It is therefore conceivable that Xylopodia is also present in similar vegetation in the intervening area between the known ranges of these two species, for example in the poorly explored Río Mantaro and Río Apurímac systems in Peru. Future explorations may turn up additional localities for this species. However, as it now stands, it appears to represent a highly unusual disjunction shown by few other plant taxa restricted to the seasonally dry forests of northwestern Peru and the eastern Andean slope in Bolivia and Argentina, corresponding to what Prado and Gibbs (1993) consider as the Pleistocene arc of tropical seasonal dry forests.

Preliminary conservation status.

As mentioned above, the actual abundance of Xylopodia is very difficult to assess, both globally and locally. Both species share a very nondescript appearance, even during flowering and especially after the shedding of leaves during the dry season. Hence, there are only very few collections. However, unlike the type species, X. laurensis is evidently more widespread and likely present in suitable habitats in between the known populations (Fig. 1 ). The estimated EOO (Extent Of Occurrence) is> 72.000 km2, resulting in a conservation status assessment of "least concern" (LC) according to the IUCN categories and criteria (2012) and guidelines (2019). Conversely, given the fact that all collections and observations made so far only report very small populations or single individuals, the AOO (Area Of Occupancy) for the species is extremely small (<0.03 km2 when applying the smallest possible grid cell of 100 × 100 m in GeoCat) presumably reflecting the narrowness of the ecological niche of Xylopodia . The latter value would consider X. laurensis as "critically endangered" (CR) according to the IUCN. These contradictory results show how difficult even a tentative assessment of a species’ conservation status can be, if the data are too limited due to either collection gaps in certain regions or taxonomic groups or real rarity of the taxon in question. At the moment, we cannot give a satisfactory answer on the threat status of X. laurensis . It might be rare and under immediate threat or maybe it has been just under collected. For the time being its conservation status must hence be categorized as "data deficient" (DD).

Figures

Figure 1. Known distribution of Xylopodia klaprothioides and X. laurensis (photo credit for La Paz: A. F. Fuentes).

Figure 2. Xylopodia klaprothioides A flower, lateral view, showing the lamellae (L) and nectar scales (NS) B flower, frontal view, showing the lamellae (L) C mature fruit with slightly opened apical valves D nectar scale in dorsal (left) and ventral (right) views E nectar scale complex with one scale removed to reveal the internal monomorphic staminodes (MS) and the inconspicuous filament flanges (FF) F sterile branches with mature leaves G xylopodium of a 2 - year-old plant H seed. All from Weigend et al. 97 / 450.

Figure 3. Xylopodia laurensis. A flower, lateral view, showing the nectar scales (NS) B flower, showing the lamellae (L) C mature fruit, showing the four apical valves D details of the central staminode (left), showing the well-developed filament flange (FF), lateral staminode (right) E staminodes within the nectar scale, showing the lateral staminodes (LS) and the central ones (CS) F plant G xylopodium. All from Martin 2887, except C (Catari 2510).

Figure 4. Habitats of Xylopodia. A deciduous forest near Jujuy, Argentina, habitat of X. laurensis B X. laurensis habitat in a dry creek near Chuquisaca, Bolivia C rocky slopes with xerophilous vegetation near the town of Contumaza, Peru, habitat of narrowly endemic X. klaprothioides.

Figure 5. False-color BSE-image of the trichome cover of the leaves of X. klaprothioides. Mineralized areas are highlighted in red, non-mineralized areas in green A abaxial surface densely covered with unicellular, glochidiate and a few scabrid trichomes B adaxial surface densely set with scabrid hairs. (Credit: H. J. Ensikat, Bonn).