Lobelia macrocentron (Bentham) Ayers (1987: 418)

Ávila-González, Heriberto, González-Gallegos, Jesús Guadalupe, Rubio-Cardoza, Jaciel & Castro-Castro, Arturo, 2018, The rediscovery of Lobelia macrocentron (Campanulaceae) after 169 years, with notes on the morphology, habitat and conservation status, Phytotaxa 374 (3), pp. 268-272 : 269-271

Lobelia macrocentron (Bentham) Ayers (1987: 418) . ( Fig. 1 ).

Heterotoma macrocentron Bentham in Hooker (1876: 68). Type:— MEXICO. Durango or Nayarit: Sierra Madre, NW of Mexico, November-February 1849–50, B.C. Seemann 2049 (holotype K!, isotype BM!).

Calcaratolobelia macrocentron (Bentham) Wilbur (1997: 562) .

Perennial rhizomatous herbs, 12–45 cm tall; stems procumbent, usually simple, green during flowering and purple during fruit maturation, pilose; leaves cauline; petiole (0.4–)1–2.5(–4.2) cm long, green to purple, pilose; blade (1–)2– 4(–6.3) × (0.5–)1.5–2(–4.8) cm, ovate to orbicular or reniform, cordate at base, rounded or acute at tip, margins subentire to dentate, green adaxially, green-purplish abaxially, pilose with slender white trichomes throughout; inflorescence a terminal corymbiform raceme, peduncle 3.5–8 cm, bracts subulate, entire, 3.5–4 × 0.8–1 mm, glabrate; pedicels 1.2– 3.5(–4.8) cm long, filiform, green with purple shades, glabrous; bracteoles absent; hypanthium asymmetrical, upper side 6.9–8 mm long, the lower side extending with corolla tissue into spur; calyx lobes subulate, (2.9–)3.7–3.9(–4.7) mm long, the two lower ones slightly shorter, positioned 0.2–1 mm above base of the spur; corolla 9–18 mm long including hypanthium; corolla tube 4.3–4.8(–6.5) mm long, white with dorsal purple lines, slit dorsally to base; corolla pink to white-pinkish, upper lobes 4–6 × 1.8–2 mm, spatulate, the lower lobes (4–)7–9.8(–12) × 2.8–3.5 mm, obovate, with two small yellow circular spots opposed to lobe sinuses at throat, narrowly divergent, apiculate; spur conicalcylindrical, 4.3–7.6 mm long measured from the base of the upper calyx lobes; staminal tube 4–5.5 mm long, glabrous, sometimes papillose; anthers 1.5–2.3 mm long, connate, blue, the three upper anthers slightly longer and curved distally toward the lower two and often covered on the backs with short slender trichomes, the two shorter anthers bearded with a white-tuft of stiff trichomes at tip; style 5.2–7.7 mm long, stigma 0.4–0.9 mm long; capsule 3–6 × 2.8–4 mm; seeds 0.4–0.7 × 0.2–0.3 mm, ellipsoid, light brown, testa sculpturing striate and shining.

Distribution, habitat and phenology:— The only precise locality known for Lobelia macrocentron is in southeastern Sinaloa ( Fig. 2 ), into the Pacific slopes of the Madrean Tropical Region, according to the Sierra Madre Occidental ecorregionalization proposed by González-Elizondo et al. (2012). In this locality, L. macrocentron was collected in a pine-oak forest, on a hillside at an elevation of 2254–2489 m. The dominant associated taxa in the arboreal stratum are Arbutus bicolor González et al. (2012: 99) , Pinus herrerae Martínez (1940: 76) , P. strobiformis Engelmann (1848: 102) and Quercus spp. Among the associated herbaceous species, Gentiana mirandae Paray (1957: 15) and Salvia lavanduloides Kunth (1817: 287) stand out. The plants were collected in flower and fruit from February to April.

Conservation status:— Lobelia macrocentron was collected in three nearby localities, each of these with abundant individuals. Using GeoCAT ( Bachman et al. 2011) the Extent of Occurrence (EOO) was of 149 km 2 and the Area of Occupancy (AOO) resulted in 8 km 2, based on cells of 2 × 2 km. According to EOO and AOO results and following the IUCN (2013) criteria (Area of Occupancy estimated to be less than 500 km 2 and known to exist at no more than three locations), a preliminary category of endangered is proposed (EN/B2a). Additionally, the population might be in danger since in the area wood extraction activities are developed, and a dam is being built 1.8 km below the base of the hill where it dwells. These activities could put the population at risk by modifying the characteristics of the habitat.

Representative specimens examined: — MEXICO. Sinaloa: Concordia, El Palmito, 23°35’11.4”N, 105°50’43.1”W, 2489 m, 8 February 2018, H. Ávila-González & J. Rubio-Cardoza 252 ( CIIDIR!, IBUG!, MEXU!) ; Ejido El Palmito, 23°35’12.69”N, 105°50’36.3”W, 2499 m, 8 March 2018, H. Ávila-González & J. Rubio-Cardoza 324 ( CIIDIR!, IBUG!, MEXU!) ; El Palmito, cerro Los Pilares, km 2.5 del camino al mirador Los Pilares, Santuario El Palmito, 23°34’24”N, 105°50’31.2”W, 2254 m, 23 March 2018, A. Castro-Castro et al. 4381 ( CIIDIR!, IBUG!, MEXU!) .

Discussion:— The Lobelia macrocentron species complex also includes L. knoblochii , L. mcvaughii , L. villaregalis and L. saturnini . This set of species can be easily separated into two groups depending on how the flowers are arranged, in racemes or solitary ( Ayers, 1987). Lobelia knoblochii , L. mcvaughii and L. saturnini share solitary flowers and spurs extending less than 4 mm beyond ovary. Meanwhile, Lobelia macrocentron and L. villaregalis share a raceme inflorescence and spurs extending 4.3–8 mm beyond ovary. The latter two species can be differentiated because the first has a procumbent habit (vs. decumbent in L. villaregalis ), longer petioles [(0.4–)1–2.5(–4.2) vs. 0.3–0.8 cm], leaves with entire to shallowly dentate margins (vs. deeply dentate), smaller bracts (3.5–4 × 0.8–1 vs. 5.5–8.5 × 3 mm), longer upper hypanthium side (6.9–8 vs. 2.5–3 mm), smaller upper corolla lobes (4–6 × 1.8–2 mm vs. 8.5–9 × 4–4.5), and narrower lower corolla lobes (2.8–3.5 vs. 6–7 mm).

The area in which Lobelia macrocentron has been rediscovered is less than 2 km from the track followed by Seemann during his exploration from Mazatlán to Durango according to his itinerary ( Seemann 1852; Fig. 2 ); hence, it is highly probable that the type locality is the same. However, it is also possible that L. macrocentron has a wider distribution and that the population from which Seemann collected might be located in another portion of that track. Regardless of this ambiguity, it is worth noting that although the surrounding areas of the old Durango —Mazatlán road are the best botanically explored places in this region, botanical novelties are constantly appearing. The type and only known locality of Lobelia mcvaughii near a scenic view called “Puerto Buenos Aires” on the old Durango — Mazatlán road is less than 20 air km northeast of L. macrocentron . The rediscovery of L. macrocentron highlights the narrow ecological preferences of the species and its vulnerability, but also that it is still critical to encourage botanical inventories in countries with such overwhelming species diversity as Mexico.

Figures

FIGURE 1. Lobelia macrocentron (Benth.) T.J.Ayers. A & B. Frontal view of pistillate-phase and lateral view of staminate-phase flower. C. Lateral view of a fruit with persistent hypanthium and spur. D & E. Terrestrial and saxicolous habit. F.Basal stems and rhizome. G & H. Leaves variation. Photographs: Heriberto Ávila-González (A–C) and Arturo Castro-Castro (D–H).

FIGURE 2. Distribution map of Lobelia macrocentron (red dots); the red line indicates Seemann’s exploration track (1849–1850) within which the original locality of the species remains unclear. The portion between Mazatlán and Durango corresponds to the old (non-toll) road, which was the only one available at that time. The star represents the town El Palmito, and the polygon of Santuario El Palmito is highlighted in green. The squares corresponds to the localities mentioned by Seemann in his itinerary (1 Mazatlán, 2 San Sebastián (currently Concordia), 3 Copala, 4 Santa Lucía, 5 El Salto, 6 Llano Grande, 7 Navíos, 8 Mimbres, 9 Durango, 10 San Francisco del Mezquital, 11 La Guajolota, 12 Santa Teresa, and 13 Tepic).