Hymenocallis ruenesiana (Amaryllidaceae), a new species from the Yucatan Peninsula, Mexico Author Ancona, Juan José Herbario UADY, Departamento de Botánica, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán. Carretera Mérida-Xmatkuil, km 15.5, Mérida, Yucatán. Mexico Author Ortiz-Díaz, Juan Javier Herbario UADY, Departamento de Botánica, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán. Carretera Mérida-Xmatkuil, km 15.5, Mérida, Yucatán. Mexico Author Durán, Kelly C. Herbario UADY, Departamento de Botánica, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán. Carretera Mérida-Xmatkuil, km 15.5, Mérida, Yucatán. Mexico Author Tun-Garrido, Juan Herbario UADY, Departamento de Botánica, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán. Carretera Mérida-Xmatkuil, km 15.5, Mérida, Yucatán. Mexico Author Palma, Geovani A. Herbario UADY, Departamento de Botánica, Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán. Carretera Mérida-Xmatkuil, km 15.5, Mérida, Yucatán. Mexico text Phytotaxa 2024 2024-04-26 645 3 270 277 http://dx.doi.org/10.11646/phytotaxa.645.3.6 journal article 10.11646/phytotaxa.645.3.6 1179-3163 13215092 Hymenocallis ruenesiana J.J. Ancona, J. Tun & Ortiz-Díaz sp. nov . ( Fig. 1 ) FIGURE 1 . Hymenocallis ruenesiana . A. Plant. B. Scape and fruits. C. Flowers. D. Fruits, a mature capsule with the seeds exposed. E. Seeds. Photographs by J.J. Ancona. Type :— MEXICO . Campeche : municipality Campeche , camino entre Chiná y Chulbac , 19°45ʹ00ʺN 90°32ʹ38ʺW , recolectado el 10 de junio de 2022, floreciendo y fructificando en cultivo el 15 mayo de 2023, J.J. Ancona & J.J. Ortiz 381 ( holotype UADY !; isotype MEXU !) . Diagnosis :— Hymenocallis ruenesiana is similar to Hymenocallis littoralis , but it is distinguished by growing in savannas and dry forests with seasonally flooded soils, being a less robust plant, barely reaching 45 cm height in anthesis, with leaves 2–3 cm wide, scape 25–37.5 cm long, perianth tube 9–11 cm long, staminal crown 1–1.2 cm long, and entire margin with apiculate center ( Table 1 ). Bulbiferous herbaceous plant, 35–40(–45) cm high; bulbs solitary or grouped, tunicate, 7–10 cm diam, tunic dark brown, membranaceous. Leaves basal, 22–35 × 2–3 cm , linear, acute, sessile, glabrous on both surfaces. Inflorescence an umbel; scape 2 per bulb, solid, spongy, 25–37.5 cm × 13.5–14.5 mm ; bracts 2, opposite, lanceolate, 5–7 cm long; flowers 12–15 per scape, sessile, actinomorphic, perianth hippocrateriform, tube straight or slightly curved, 9–11 cm long, lobes 6, linear, subequal, reflexed, 9–12 cm long, white; stamens 6, filaments connate at the base forming a staminal cup, staminal cup 1–1.2 cm long, staminal cup diameter 1.5–2 cm with entire margin, apiculate among connate filaments, the free parts 4.5–5.5 cm long, filiform, inserted into the margin of the staminal cup, green for most of their length, white at base, anthers dorsifixed, introrse, longitudinally dehiscent, linear, ca 12 mm long, yellow; ovary inferior, 3-locular, ovules 4–8 in each locule, style 19–22 cm long, solitary, filiform, stigma capitate. Fruit a fleshy capsule when young, membranaceous when ripe, dehiscent, 2–2.5 cm long; seeds 6, 2 per locule rarely 3, reniform, fleshy, 1–1.7 cm long, 0.8 cm width, green. Eponymy :—The specific epithet of this species is dedicated to Rocío Ruenes Morales, a researcher at our campus at the Universidad Autónoma de Yucatán ; specialist in Ethnobotany of the Yucatan Mayan culture. Geographic distribution and habitat: So far Hymenocallis ruenesiana is known only from the states of Campeche and Yucatán ( Fig. 2 ). Therefore, it can be considered as an endemic species of the Yucatan peninsula. It inhabitis savannas and dry forests with seasonally flooded soils ( Fig. 3 ), at elevations from 8 to 150 m . FIGURE 2 . Distribution map of Hymenocallis ruenesiana (blue triangles) and Hymenocallis littoralis (red dots) in the Yucatan peninsula, Mexico. Phenology:— Flowering from May to October; fruiting from May to November. Taxonomic remarks:— Hymenocallis ruenesiana is known only from the dry forests with seasonally flooded soils and savannas of the Yucatan Peninsula. Tolerating flooded soils in the rainy season. It is a small plant compared to H. littorallis ( Table 1 ). FIGURE 3 . Hymenocallis ruenesiana in its natural habitat: A. Savanna Chacho Lugo, Tekax, Yucatán, Mexico; B. Savanna Chulbac, China, Campeche, Mexico. C. Seasonally dry forest of the Puuc region, Oxkutzcab, Yucatán, Mexico. Photographs by J.J. Ancona and W.J. Hayden. TABLE 1 . Morphological comparison between Hymenocallis littoralis and Hymenocallis ruenesiana from the Yucatan peninsula.

Character	H. littoralis	H. ruenesiana
Height of the plant in anthesis	70–120 cm	35–40 (–45) cm
Leaf shape	Lorate	Linear
Leaf: length × width	50–100 × 3.5–6 cm	22–35 × 2–3 cm
Inflorescence	1 per bulb	2 per bulb
Scape length	60–90 cm	25–37.5 cm
Perianth tube length	13–15 cm	9–11 cm
Margin of the staminal cup	Dentate	Entire with apiculate center
Staminal cup length	2.5–3.3 cm	1–1.2 cm
Staminal cup diameter	3–3.5 cm	1.5–2 cm
Seed: length × width	2.5–3×1.5 cm	1–1.7–0.8 cm
Habitat	Coastal dunes	Savannas and dry forests with seasonally flooded soils

In herbarium collections, identifying and differentiating these two species is very difficult as most collections are poorly preserved. In several specimens no details of the staminal cup are observed, while other specimens have incomplete leaves and scapes, therefore the total length cannot be known. Among the well-preserved specimens with visible diagnostic characters, two distribution patterns of the genus Hymenocallis were detected in the Yucatan peninsula. The new species presents distribution inland of the Yucatan peninsula, dry forests with seasonally flooded soils and savannas at altitudes from 8 to 150 m . While H. littoralis , as its name points out, is distributed along the coastline of the Yucatan Peninsula, in sandy soils of coastal dunes. Even in the original description of Pancratium littorale (= Hymenocallis littoralis ), Jacquin describes that it grows abundantly in the coastal dunes of Cartagena, Colombia . In herbarium collections, specimens of H. littoralis were identified inland the Yucatan peninsula, but they were considered as cultivated and ornamental. On the other hand, the specimen P. Moreno 842 deposited in the MEXU herbarium, is determined as Hymenocallis acutifolia Sweet (1830: 513) . However, H. acutifolia is a species distributed in the Transmexican Volcanic Belt province and Sierra Madre del Sur province sensu Morrone (2014) , at elevations between 1500 and 2,500 m . Furthermore, H. acutifolia only produces four flowers per scape compared to the Hymenocallis from the Yucatan peninsula, which produce more than 12 flowers per scape. The specimen P. Moreno 842 is difficult to determine since the plant was poorly collected, with incomplete leaves, without scape and a single flower that does not show detail of the staminal crown. In addition, the label does not present precise information on the locality and the ecological environment where the plant was collected; but what is certain is that it is not H. acutifolia . Conservation status: — Hymenocallis ruenesiana has an AOO of 48 km 2 and an EOO of 19.104 km 2 . According to the Effective Occupancy Area (EOO), the category was ‘Vulnerable’ (VU), while according to the Apparent Occupancy Area (AOO), the category was ‘Endangered’ (EN). Because the species is rare, its AOO is small, the species only occurs naturally in nearly intact vegetation, and most of its known populations occur in savannas and rainforests with low anthropogenic impact. However, the exploitation and deforestation of these ecosystems to become livestock or agricultural areas would endanger this species. Such is the case of the populations of the savanna Chacho Lugo, which has been impacted by the agriculture of the “Mennonite” groups. Palynological exploration :—Grains in monads; monocolpate and heteropolar; with bilateral symmetry. Elongate to oblong ( H. littoralis ) and oblong to elliptic ( H. ruenesiana ), very large grains with heterobrochate exine ( Fig. 4 ). The main pollen body (corpus) is characterized by reticulate ornamentation with large size lumina and clavate outgrowths at irregular intervals. At the equatorial ends of the pollen grain (cappus), ornamentation is abruptly modified by small lumina. Exine thickness in the corpi region is 4.63 μm–7.78 μm and in the cappus region 3.23 μm–5.36μm. FIGURE 4 . Scanning electron microscope (SEM) micrographs of pollen grains of A) Hymenocallis littoralis and B) H. ruenesiana . Scale bar= 20 μm. Although pollen size and shape are considered traits of secondary importance, in some cases, they can delimit species. In the genus Hymenocallis , a positive correlation between style length and pollen size has been observed among several species ( Meerow & Dehgan 1985 ). In Venezuela , Martín et al. (2012) analyzed the size and morphology of pollen grains of Hymenocallis species and concluded that these characters allow delimiting endemic species from those with a wide distribution. In the case of the Yucatan Peninsula, the morphology and dimensions of the pollen grains present a morphological discontinuity between the two species of Hymenocallis . Among the specimens analyzed we can distinguish between elongated, oblong and elliptical shapes. In H. littoralis the pollen grain has an elongated to oblong shape while in H. ruenesiana we can find oblong to elliptical pollen grains. Here it is important to mention that herbarium specimens presented pollen with oblong shapes while pollen from live plants presented an elliptical shape. We recommend a more complete study to compare pollen grains using only living plants, since the herbarium drying process might be influencing the morphology of pollen grains in Hymenocallis species. Specimens examined :— MEXICO . Campeche : municipality Campeche , camino entre Chiná y Chulbac , 19°43’40’’N 90°33’54’’W , recolectado el 10 junio de 2022, floreciendo y fructificando en cultivo el 15 mayo de 2023, J . J . Ancona & J . J . Ortiz 382 ( UADY ) ; Unidad de Evaluación y Monitoreo de la Biodiversidad de Hampolol , 19°56ʹ09ʺN 90°22ʹ40ʺW , 20 June 1996 , P . Zamora & D. Méndez 5108 ( MEXU ) ; San Antonio Ebulá , 19°48ʹ11.4ʺN 90°36ʹ28ʺW , elev. 19 m , 8 July 2003 , C . Pavón-Lanz 607 ( MEXU ) ; municipality Calakmul , 6 km rumbo a Nuevo Becal , 18°35ʹ5ʺN 89°2ʹ10ʺW , elev. 270 m , 2 October 1997 , G . Bacab W . 130 ( MEXU ) ; a 16 km al NW de Dos Lagunas , 18°57ʹ20ʺN 89°23ʹ55ʺW , elev. 170 m , 22 May 1998 , E . Martínez S . et al. 30971 ( MEXU ) ; municipality Calkiní , 12 km al E de Tancuché , cerca del Rematesobre el camino Calkiní-Punta Arenas , 26 July 1987 , E . Cabrera 13932 ( MEXU ) ; municipality Escárcega , south end of isla Silvituk , 18°30ʹ00ʺN 90°17.5ʹ00ʺW, elev. 40 m , 26 July 1996 , D. L . Lentz 2630 ( MEXU ). Yucatan : municipality Celestún , 16 km en la carretera Celestún , 20°52ʹ00ʺN 90°24ʹ00ʺW , 07 April 1996 , L. Parrilla 3 ( UADY ) ; municipality Celestún , 16 km en la carretera Celestún , 20°52ʹ00ʺN 90°24ʹ00ʺW , 04 April 1996 , T . Barreiro 05 ( UADY ) ; municipality Celestún , 83.5 km carretera Mérida-Celestún , 28 May 2007 , S . May & C . Castillo 07 ( UADY ) ; municipality Celestún , Celestún-Bella Flore km 16, 20°52ʹ00ʺN 90°6ʹ00ʺW , 7 April 1996 , E . Regalado 31 ( UADY ) ; municipality Oxkutzcab , Rancho Kiuic , 20°5.79ʹ00ʺN 89°33ʹ00ʺW, elev. 100 m , 9 June 2003 , W . J . Hayden & Ch. McKenney 4712 ( UADY , CICY ) ; municipality Tekax , carretera Becanchen-Nohalal , 19°46ʹ38ʺN 89°13ʹ10.7ʺW , elev. 67 m , 29 September 2016 , C . Benites et al. 2 ( UADY ) .