Xanthosoma gratiae Cornejo & Croat, 2022

Cornejo, Xavier & Croat, Tom, 2022, Xanthosoma gratiae (Araceae), a new species from the cordillera ChongónColonche in coastal Ecuador, Phytotaxa 558 (2), pp. 237-242 : 238-241

Xanthosoma gratiae Cornejo & Croat , sp. nov. ( Fig. 1 )

Xanthosoma gratiae differs from all species in the group Chamaexanthosoma by the colour of the spathe blade which is yellowish-green to light yellow or yellowish-cream without, and the leaf blades with obtuse apex. Xanthosoma gratiae is similar to X. perssonii Delannay, Cornejo & Croat , but also differs by the length of the spadix with a shorter staminate portion 7.0– 10.5 cm long (vs. 14 cm long), a shorter pistillate portion 2.5–3.0 cm long (vs. 4 cm long), and the consistently light green (vs. dark purple) spathe tube inside.

Type: — ECUADOR. Guayas: Casas Viejas, cerca al límite noroccidental del Bosque Protector Cerro Blanco, ca. 10 W from Guayaquil , 02°07’S 25’’S, 80°05’43’’W, ca. 240 m, seasonally deciduous dry forest, 12 Feb 2022 (y. fl), fully flowered in cultivation in Guayaquil, 02°07’46”S, 79°54’25”W, ca. 6 m, 16 Feb–7 Mar 2022 (fl), X. Cornejo, J. Josse & L. Alcívar 10019 (holotype GUAY!, mounted material and spirit collection) .

Stemless tuberous herb to 0.5 m tall; tuber depressed-oblate, drying ca. 6 cm diameter. Prophylls (only one seen) oblong-lanceolate, membranous, 2-costate, ca. 9 x 1.4 cm, subhyaline creamish-white, the costa yellowish. Leaves erect to erect-spreading; petioles 30–60 cm long, sheathed 1/3 to less than ½ its length, light-green, drying dark brown, 3–4 cm diam. near the base, 9–10 mm diam. midway, 7–9 mm diam. near the apex; blades spreading to somewhat reflexed, ovate-cordate, 30–40 cm long, 20–32 cm wide, 1.2 to 1.6 as long as wide, 0.5 times as long as petiole, broadest across the posterior lobes, upper surface middle green, slightly sulcate to flat and glossy along veins, drying thin, brownish green, glabrous above, paler green and medium-glossy throughout, primary lateral veins 4–5 per side, prominent, strongly and concolorous below; slightly to broadly obtuse and apiculate at apex (apiculum 1–3 mm long), prominently lobed at base; anterior lobe 20–30 cm long, margins straight to slightly convex, entire; posterior lobes 9– 19 cm long, 9–18 cm wide, obtuse to rounded, often overlapping at the base; basal veins 5–6 pairs, 1 st pair free to base, 2 nd basioscopic; posterior rib not naked, branching before reaching the tip of the posterior lobe; sinus up to 1 cm width at base. Inflorescences 1 per axil, erect; peduncle 30–47 × 1.2–1.5 cm, pale green, glossy when fresh; spathe 15–21 cm long, tube middle green, slightly glossy, inconspicuously and finely sulcate longitudinally outside (observable under magnifying glass), light green with weak longitudinally veins, glandular within, 3.5–5.5 × 2.0– 2.6 cm when fresh, 4 × 1.4 cm when dry; blade yellowish-green to light yellow or yellowish-cream outside, creamish-green to creamish-white inside, 8–14 cm long when fresh, 7–11 cm when dry; spadix 14–18 cm long, staminate portion 7.0–10.5 × 1.3–1.4 cm and white when fresh, 6–8 × 0.8–1 cm when dry, sterile portion fully covered by staminodia, these 3.5–4.5 cm long, 7–8 mm diam. in the middle, c. 3.5 × 0.2 cm when dry, white, the lower part with thickened staminodia 2.5–5.0 mm long when fresh, white or light brownish-pink; pistillate portion 2.5–3.0 × 1.1–1.4 cm and yellowish-white to creamish-yellow when fresh, 2 × ca. 0.9 cm when dry. Infructescences not seen.

Discussion: — Xanthosoma gratiae as a member of the Chamaexanthosoma group can be recognized from all remaining species in the group by the spathe blade being yellowish-green to light yellow or yellowish-cream at maturity without and the leaf blades with an obtuse apex. Within the species of this group, the fully light green spathe inside is only shared with X. guayaquilense Delannay, Cornejo & Croat (2019:158) , but X. gratiae differs at first sight from the latter species by the leaf blade shape, apex, size, arrangement and absence of pubescence. By the stemless habit, the leaf blades ovate-cordate of similar sizes with 4–5 pairs of primary lateral veins and the usually overlapping posterior lobes, Xanthosoma gratiae may resemble X. perssonii Delannay et al. (2019:160) , but in addition to the distinctive aforementioned characters the former species also differs from the later by the consistently light green inner spathe tube color (vs. dark purple), the spadix of shorter length, and different life zone. Xanthosoma gratiae may also resemble X. daulense Croat & Delannay (2017:152) s.s., another endemic to the Guayas province that also belongs to the same Chamaexanthosoma group, but the new species, in addition to the mentioned distinctive colors of spathe also differs from the latter by the leaf blades ovate-cordate, broader, with the inner sinus up to 8 mm width, otherwise usually closed, and the blade apex obtuse and apiculate.

In the original publication of X. daulense , the selected holotype, Harling 4801 (S), consisted of a leaf blade without petiole and a detached spathe blade, the remaining reproductive parts of inflorescence are missing, the distinctive full colors of spathe are handwritten by Harling himself in the mounted type label as: ¨Spathe green at base, white in its upper part, violet red in the throat¨. As the original description of X. daulense has been based on the fragmentary poor holotype and only one fertile paratype (Cornejo & Bonifaz 989, GUAY), the description of this species is mostly based on the only cited paratype (Cornejo & Bonifaz 989, GUAY), that was gathered at the north of cordillera Chongón Colonche in western Ecuador. However, the discussed paratype of X. daulense morphologically and phytogeographically fits well within X. gratiae , a species that was found at the southeastern terminal end of the same mountain range. In contrast, the type locality of X. daulense was from a different ecosystem at the altitudinally lower Guayas basin watershed. Recently, a not previously known fertile isotype of X. daulense that was not included in the original publication of the species has been found at MO, the images are posted in Tropicos (https://www. tropicos.org/name/100442254). The mentioned isotype adds additional valuable information on the inflorescence and leaf blade of X. daulense s.s. that allow us to understand the real boundaries of the species and makes clear after studying X. gratiae in the field and in cultivated material that the original description of X. daulense is composed of intermixed traits of the two closely related species discussed herein. Therefore, the cited paratype (Cornejo & Bonifaz 989, GUAY) of X. daulense is here recorded as belonging to the new species X. gratiae , and X. daulense s.s. is regarded as a validly published poorly known species closely related to X. eggersii ( Croat et al. 2017; see Table 1 ).

Etymology: —The epithet gratiae that is in Latin means beauty of form and manifestation of a favor. This refers to the nice appearance of the plant and largely to the fact that while exploring in the field the new species was found just few minutes after the type collector specifically asked Yeshua if a new species still could be found in a highly disturbed habitat as the type locality.

Habitat and distribution: — Xanthosoma gratiae is known only by two collections gathered between ca. 240 m to 500 m, at the north and southeast of cordillera Chongón-Colonche , that is an extra Andean mountain range , in a seasonally disturbed Pacific dry and transitional to moist forests west to northwest from Guayaquil , in the provinces of Guayas and Manabí, in coastal Ecuador. It is expected to be found on the western side of Cerro Blanco private reserve. Xanthosoma gratiae occurs on dark-chocolate clayish soils that are a superficially rich in organic matter, but abundantly rocky and lighter ferruginous-brown in deeper layers. The presence of tubers that have the ability of sprouting during the rainy season throughout years makes this species a seasonally persistent herb on disturbed habitats.

Phenology and cultivation: —Vegetatively growing and flowering from February to March, accomplishing full life cycle once in a year, during the rainy season only. Similar to X. guayaquilense Delannay, Cornejo & Croat and the sympatric X. diazii Croat & Delannay (2017:164) , both also endemics to the seasonal Pacific dry forests of coastal Ecuador. The phenology of X. gratiae is triggered at the beginning of rainy season, induced by the changes of weather parameters such as increase in environmental moisture, regional temperature, and presence of rains. The whole aerial part of the plant fades in April before the end of rainy season, and the species is apparently absent during the dry season from June to December. During this period, the total absence of rain generates a marked stress effect on native vegetation that exhibits a strongly deciduous behavior and conspicuously transforms the habitat and landscape where X. gratiae occurs, from a luxuriant green appearance to predominantly leafless and grayish-opaque which is in contrast to the scattered evergreen floristic elements, among which, the tubers of X. gratiae remain undetected few centimeters underground waiting for the next seasonal changes that will allow them to sprout and grow again.

It has been observed that the glandular tissue at the inner spathe tube behind the pistillate portion segregates a hyaline exudate at same time as the stigmas are wet and the inflorescence produces scent near midnight.

Xanthosoma gratiae is one of the few native herbs that can be cultivated as an ornamental under shade in tropical warm cities as Guayaquil. The new species can be reproduced by propagules or vegetative seedlings. Therefore, efforts for conservation of this endangered new species must consider the vegetative propagation and cultivation as a seasonal ornamental plant.

Conservation status: —The less than 20 individuals found in the habitat that is threatened by selective cutting and occasionally fires during the dry season and mainly by the unstoppable urban expansion of the city of Guayaquil corelated to the low regional level of appreciation for native species and nature led us to regard Xanthosoma gratiae as Critically Endangered CR B1 ab(iii), CR C 2 a(ii) ( IUCN 2022). The high sensibility to the current seasonal changes of weather parameters that drives the phenology of X. gratiae suggest that this and other related endemics as X. guayaquilense and X. diazii , that exhibit a similar extreme seasonal behavior may be affected by global climatic change. Therefore, the survival of these seasonally cryptic endemic herbs from coastal Ecuador facing climatic change is uncertain.

Paratype: — ECUADOR. Manabí: Crucita, Cuenca del Río Ayampe , 01°39’W, 80°38’W, 500 m, 9 Dec 1993 (fl), X. Cornejo & C. Bonifaz 989 (GUAY!) .

Figures

FIGURE 1. Xanthosoma gratiae Cornejo & Croat. A, Inflorescence with closed spathe tube, anterior view; B, Inflorescence with open cut spathe tube, anterior view; C, Spathe, note the yellowish-green color at upper two thirds, posterior view; D, Fertile stamens; E, Close up of inner spathe tube exhibiting translucent microdroplets of glandular exudate; F, Plant with fully mature ovate-cordate leaves in an open environment in the type locality; G, Close up of pistillate inflorescence and lower staminodes, note the full green color of spathe tube inside, anterior view.