Pisonia horneae Trejo & Caraballo, 2017

Caraballo-Ortiz, Marcos A. & Trejo-Torres, Jorge C., 2017, Two new endemic tree species from Puerto Rico: Pisonia horneae and Pisonia roqueae (Nyctaginaceae), PhytoKeys 86, pp. 97-115 : 98-100

Pisonia horneae Trejo & Caraballo sp. nov. Figs 1 , 2 , 3 , 4

Pisonia subcordata sensu Heimerl and Urban (1905), not Swartz (1788).

Pisonia subcordata Swartz var. typica Heimerl f. gigantophylla Heimerl, Bot. Jahrb. Syst. 21: 630. 1896. Pro parte (see Additional specimens examined section).

" Pisonia woodburyana Proctor", nomen nudum.

Type.

PUERTO RICO. Municipality of Quebradillas, Bo. Terranova, old train road to El Tunel Negro, from Highway #2, border of dirt road near GPS [18.4840°, -66.9536°], 5 m, 12 Jul 2003, J.C. Trejo, P. Vives, A.M. Camacho, and M.A. Caraballo 2310 (holotype: UPR!; isotypes: FLAS! [#230768, 230769]) .

Diagnosis.

Pisonia horneae is distinguished from congeners from Puerto Rico by a combination of the following characters: leaves membranaceous and puberulous, twigs puberulous, fruits elliptic-oblanceolate and grayish with 10 rows of viscid glands along their whole length.

Description.

Trees dioecious to 10 m high with trunks to 30 cm in diameter. Bark finely and vertically striated, hazel, grayish, or silvery, sometimes lustrous, with lenticels about 3 mm in diameter. Twigs slightly ancipitous, greenish, and puberulous when young; terete, puberulent, and grayish when old. Leaves deciduous, clustered towards the ends of branches; opposite or subopposite, decussate; petioles to 7 cm long, grayish; blades ovate, elliptic, obovate, or roundish, sometimes asymmetric, 9-26 (-30) × 11-16 (-20) cm, apex acute to rounded, sometimes cuspidate, base acute to rounded, sometimes cuneate, cordate, or oblique, margin entire or wavy; adaxial side glabrous or puberulent; abaxial side puberulous, 0.1-0.4 mm long; chartaceous, drying membranaceous, brittle, light green above, paler below; veins pinnate, reticulate, secondary veins arcuate, up to twelve pairs, opposite or alternate, pale brown; abaxially pubescent and raised up to the secondary ramifications, main vein purplish on young plants. Inflorescences terminal or axillary, dendroid, to 7 cm long, pale green, puberulous; crown compact, flabellate; Flowers slightly fragrant; staminate flowers campanulate at anthesis, greenish white, 4 mm long; pistillate flowers cylindrical-campanulate at anthesis, 2 mm long. Infructescences dendroid, 10-16 cm long, drying grayish; peduncle terete, angled at base; crown lax, branches forked or pseudo-dichotomous; terminal branches with minute subulate bracteoles close to the anthocarps. Fruits anthocarps (achenes), elliptic to oblanceolate, 10-13 × 3 mm, longitudinally striate, tip cuspidate; husk softly ligneous, about 0.3 mm thick, with ten lines of viscid glands over ribs along its whole length, puberulous; glands capitate, about 0.5 mm long.

Habitat and ecology.

Pisonia horneae is found in moist limestone forests at low elevations in the Northern Karst of Puerto Rico (10-150 m; Fig. 3 ), frequently on slopes and forest edges with relatively undisturbed vegetation. In eastern Puerto Rico, the species have been recorded from volcanic moist substrates from approximately 10 to 300 m (Fig. 3 ).

Although P. horneae is a species from low elevations and can grow near the coast, it has not been observed as part of the coastal vegetation. In contrast, the congener P. subcordata is distributed on coastal zones directly exposed to sea spray on elevations typically less than 10 m.

Phenology.

Pisonia horneae sheds leaves during March and April. After shedding, the plant usually produces flowers by April, though flowers have been also recorded in January. Fruits have been recorded in May and June.

Vernacular names.

As with other tree species of Pisonia from Puerto Rico, P. horneae is locally known as corcho.

Etymology.

We are honored to dedicate this species to Frances Elvira Worth Horne (1873-1967), an American illustrator who lived in Puerto Rico and, for 45 years, painted its plants and birds. Ms. Horne composed 750 watercolors of Puerto Rican plants to complement Nathaniel Lord Britton’s Flora Borinqueña ( Jackson 1997), a popular book on common plants of Puerto Rico which was never published. Only 44 of her plant watercolors were published in the botanical journal Addisonia from 1922 to 1932 (Jackson, 1997), while 48 were included in the book Common Trees of Puerto Rico and the Virgin Islands ( Little et al. 1977). She donated her collection of plant watercolors to The New York Botanical Garden in 1963 ( Jackson 1997), which can be consulted at http://plants.jstor.org [accessed 02.08.2017]).

Abundance and conservation.

Pisonia horneae can be considered a rare to locally occasional species. Despite its broad distributional range along the Northern Karst of Puerto Rico, trees of P. horneae are usually found isolated or forming small groups. The only localities where we have observed the species as locally common include a few karstic ravines in the municipality of Quebradillas and some limestone hills with relatively undisturbed forest in Ciales (Bo. Hato Viejo) and Dorado (Bo. Rio Lajas). Pisonia horneae seems to be extremely rare outside the Northern Karst, as the species is only known from three scattered localities in eastern Puerto Rico in the municipalities of Rio Grande, San Lorenzo, and Yabucoa. In Rio Grande, P. horneae seems to be uncommon and is only known from a single specimen (described below) and an unvouchered observation of a solitary sapling made in 2006 by biologist J. A. Sustache from the SJ Herbarium (pers. comm.). The authors visited the historical locality of Cerro Gregorio in San Lorenzo in December 2016, but no Pisonia were located. The locality in Yabucoa contained a single individual; however, it was fruiting and multiple seedlings were observed around the tree, suggesting the presence of additional individuals at the site (see Discussion section).

Additional unvouchered localities where P. horneae has been reported include Arecibo (Bo. Cambalache, Cambalache State Forest, 30 m, 25 Jul 2007, MACO), Bayamón (Bo. Volcán, 45 m, 26 Dec 2007, MACO; Bo. Juan Sánchez, Parque Julio Enrique Monagas, 35 m, 13 Jan 2008, MACO) and Carolina (Bo. Hoyo Mulas, 10 m, 07 Feb 2008, MACO and N.I. Cacho).

Pisonia horneae is currently designated as a critical element of the flora of Puerto Rico by the Department of Natural and Environmental Resources of The Commonwealth of Puerto Rico (listed as P. woodburyana ) ( DNER 2008). It is also preliminary considered as an “Imperiled” (sensu NatureServe) or “Vulnerable” (sensu IUCN Red List) species by Gann et al. (2015-2017).

Additional specimens examined.

PUERTO RICO. Arecibo: Cambalache, 50 m, 19 Jan 1989, Liogier 36633 (NY, UPR); Bo. Dominguito, Mata de Platano Biological Station , 93 m, 25 Jul 2003, Trejo 2349 (UPR); 142 m, 25 Jul 2003, Acevedo-Rdgz. 13404 (FTG, US); 140 m, 12 Jan 2016, Caraballo and Rivera 3380 (PAC, UPR); Finca El Tallonal, 101 m, 15 Aug 2003, Trejo 2364 (UPRRP); 100 m, 16 Mar 2004, Trejo 2585 (UPR); Bo. Miraflores, sector Biáfara, Finca Dentón, 175 m, 14 Sept 2003, Trejo 2397 (UPR); 169 m, 28 Nov 2003, Trejo 2482 (UPR) ; Bayamón: 21 Feb 1959, Woodbury s.n. (NY [#00680786], UPR [#000772]); Bo. Hato Tejas, 45 m, 21 May 2009, Caraballo et al. 2871 (UPR) ; Canóvanas: Bo. San Isidro, 10 m, 2 Jan 2017, Caraballo 3382 (PAC) ; Ciales: Bo. Hato Viejo, 160 m, 9 Jun 2007, Caraballo et al. 1818 (UPR); 130 m, 9 Jun 2007, Caraballo et al. 1822 (UPR) ; Dorado: Bo. Higuillar, 8 Feb 1964, Liogier 10670 (F, MAPR, NY); Bo. Sabana, northeast of Regadera , off Road 691, 5- 10 m, 12 May 1985, Proctor 41173 (UPR); Bo. Río Lajas, 15 m, 20 Jun 2003, Trejo and Caraballo 2279 (UPR) ; Hatillo: Bo. Capáez, ca. 5 m, 12 Jan 2006, Axelrod 13357 (UPRRP) ; Isabela: Quebrada La Sequia , 75 m, 2 Oct 2005, Caraballo et al. 639 (UPR); Guajataca gorge, 75 m, 26 Jan 2006, Caraballo et al. 1425 (UPR); Cordillera Jaicoa, 200 m, 23 Aug 2006, Caraballo 1196 (UPR) ; Loíza: Bo. Piñones, Piñones Forest Reverse, 13 Mar 1980, Del Llano s.n. (UPRRP [#96]) ; Manatí: Bo. Tierras Nuevas Saliente, 03 May 2001, Axelrod and Zachariades 11754 (UPRRP); Bo. Tierras Nuevas Poniente , Hacienda La Esperanza , 10 m, 14 Mar 2006, Caraballo et al. 919 (UPR); 12 m, 28 Mar 2006, Caraballo and Rivera 976 (UPR) ; Moca: Bo. Aceitunas, 175 m, 1 Mar 2008, Caraballo 2455 (UPR) ; Quebradillas: Bo. San José, Quebrada Bellaca, 52 m, 14 Oct 2003, Trejo and Caraballo 2444 (UPR); Bo. Cacao-Terranova, Quebrada Las Talas [El Gallo], 85 m, 21 Aug 2004, Trejo and Caraballo 2751 (UPR); Bo. Cocos, Quebrada Bellaca, 101 m, 9 Mar 2005, Trejo et al. 2873 (NY, UPR); limestone hills, ca. 150 m, 22 May 2005, Axelrod et al. 13062 (UPRRP) ; Río Grande: Rio Mar, 100 m, 5 Aug 1988, Liogier and Martorell 36637 (NY, UPR) ; San Lorenzo: Prope Hato Grande in sylva primaera montis Gregorio, 31 Aug 1885, Sintenis 2705 [mixed specimens, see Introduction and additional specimens examined for P. roqueae ] (B [10-0217019]; GH [00037445]; K [K000036122]) ; Toa Baja: Bo. Candelaria, E sector, Mogotes de Nevarez , 20-90 m, 27 Mar 1989, Proctor 45450 (US); 5 Mar 1914, Britton et al. 1515 (NY); Campanillas, 8 Jan 1959, Woodbury s.n. (UPR [#027151]); Nevárez, 75 m, 16 Mar 2006, Caraballo et al. 931 (UPR) ; Vega Alta: Bo. Espinosa, 11 Feb 1926, Gleason and Cook A 134 (NY); Bo. Sabana, 5-10 m, 12 May 1985, Proctor 41173 (IJ); hill NE of Regadera, 5 m, 1 Apr 1987, Proctor 43284 (US); Bo. Regadera , Axelrod 84 (UPRRP) ; Yabucoa: Cuchilla de Pandura, 175 m, 13 June 2006, Caraballo and Flecha 1088 (UPR); Without locality: without locality, 8 Nov 1886, Sintenis 4355 [see Introduction and additional specimens examined for P. roqueae ] (B, n.v., probably lost) .

Figures

Figure 1. Pisonia horneae. A Branch showing adaxial side of leaves B Abaxial side of leaves C Staminate (left) and pistilate (right) flowers at anthesis D Seedlings E Bark F Lower trunk of an adult tree. Note the characteristic swollen base observed in all Pisonia from Puerto Rico, where the trunk base wraps over the rocks as it grows. Photo credits: A-B, E-F: JCTT; C-D: MACO.

Figure 2. Isotype specimen of Pisonia horneae from the University of Florida Herbarium (Trejo et al. 2310, FLAS [230768]). Photo courtesy of The University of Florida Herbarium (FLAS) - Florida Museum of Natural History.

Figure 3. Distribution of Pisonia (excluding P. aculeata) in Puerto Rico and adjacent islands based on herbarium specimens. Empty symbols represent historical localities where populations have been presumably extirpated (see Trejo-Torres 2005 and this study for details).

Figure 4. Fruits of the six species of Pisonia from Puerto Rico. A P. aculeata B P. albida C P. horneae D P. roqueae E P. subcordata F P. taina. Reference specimens: A Rose 3548, US B Little 13219, US C Acevedo-Rdgz. 13404, US D Proctor 44432, US E Breckon 7766, US; and F Trejo 2371, US.