Two new species and a new combination in Protium (Burseraceae) from Costa Rica

Abstract Two new species of Protium (Burseraceae) are described and illustrated: Protium aguilarii sp. nov., from the Pacific slope of the Osa Peninsula, Puntarenas Province, Costa Rica; and Protium hammelii sp. nov., from wet forests on the Caribbean slopes of Nicaragua and Costa Rica. In addition, Protium brenesii comb. nov., is proposed as a new combination based on Trichilia brenesii, a name that was based on a specimen collected with flowers in the mountains near San Ramón, Alajuela Province, Costa Rica. It is compared with Protium costaricense, a similar species with which it has been confused for more than 90 years. Finally, illustrations and specimen citations are provided for all the aforementioned taxa, and some others with which they have been confused.


Introduction
Th e genus Protium (Burseraceae), with approximately 160 species, is nearly pantropical in distribution, though absent from continental Africa. Twelve species (including those described in this paper) have been recorded from Costa Rica, making this the largest of the fi ve native genera in the country. Protium is distributed in Costa Rica from sea level to 1500 m, mainly in humid lowland forests, though some species occur in montane forest or (more rarely) relatively dry areas [e.g., P. tenuifolium Engl. subsp. sessilifl orum (Rose) D. M. Porter on the Pacifi c slope]. Th e genus is characterized in general by its arborescent or less often shrubby habit; resin that is usually aromatic; imparipinnately compound, trifoliolate, or rarely unifoliolate leaves, with petiolules that are commonly pulvinulate at both ends, (3) 4-5-merous fl owers with distinct or weakly connate petals and 8-10 stamens inserted outside the base of the nectary disk, and dehiscent fruits with 1-5 pyrenes.
Th e two new species described below and the need for a new combination in Protium were discovered during preparation of the Burseraceae treatment for the Manual de Plantas de Costa Rica. Th is study was based on an examination of Protium specimens deposited at A, CR, F, GH, MO and USJ (acronyms according Th iers 2016, continually updated), along with consultation of digital images in national and international virtual herbaria and relevant literature on Protium (e.g., Rose 1911;Standley 1937;Swart 1942;Standley and Steyermark 1946;Cuatrecasas 1957;Porter 1970;Daly 1987Daly , 1989Daly , 1997Daly , 1999Daly , 2002Daly , 2014Daly , 2016Porter and Pool 2001). Additional fi eld collections were conducted in Costa Rica in February through March 2016. Th e distribution map was generated using the program SimpleMappr (Shorthouse 2010) from coordinates reported on specimen labels; specimens whose label data did not indicate coordinates are shown in brackets.
Habitat and distribution. Protium aguilarii is endemic to Costa Rica, where it is restricted to the Osa Peninsula, on the southern Pacifi c coast in Puntarenas Province. It occurs in primary forest, at 150-400 m elevation. In Aguabuena, Rincón de Osa, this species occurs in well-drained forest on undulating terrain, with many palms and large lianas; here, it co-occurs with Brosimum utile (Kunth) Oken (Moraceae), Carapa Aubl. (Meliaceae), and Symphonia L. f. (Clusiaceae) (see, for example, K. Th omsen 226). In Rancho Quemado, P. aguilarii is a small, infrequent tree on mountain ridges, where it is sympatric with tree species that are not very common in the area, or even the country as a whole, including Phenology. Protium aguilarii is known from only six fertile collections (one of these with fl owers in bud). Pistillate fl owers have been collected in April, and fruits in February, May, June, and December.
Common name. Copalillo (Spanish; Costa Rica, K. Th omsen 683). Etymology. Th e epithet of this new species honors Reinaldo Aguilar Fernández for his important contributions to botany and his dedicated study and devoted collection of the plants of the Osa Peninsula for more than 25 years. He has become the world's expert in the fl ora of this remarkably species-rich and beautiful corner of the world. Th is species is further dedicated to him in appreciation of his support and intellectual stimulation.
Discussion. Protium aguilarii can be recognized by the combination of leaves with 5-9 leafl ets with hispidulous pubescence on the petiole, rachis, petiolules, abaxial side of the leafl ets, and infl orescence axes; leafl ets with a distinct marginal vein that is visible on the abaxial side; short infl orescences and infructescences; fl owers that are 4-merous, with the petals appressed-pubescent on the abaxial side and glabrous on the adaxial side; and glabrous pistils. Th e new species resembles, and has been confused with, P. costaricense, which, as treated here, is known only from the Caribbean slope of Nicaragua, Costa Rica, and Panama. Both species share hispidulous pubescence on the leafl ets and infl orescences, but P. aguilarii has a glabrous pistil (vs. densely pubescent in P. costaricense), short infl orescence (ca. 0.6 vs. 1.6-6.5 cm long), petals that are glabrous on the abaxial side (vs. sparsely pubescent), and secondary venation brochidodromous (vs. eucamptodromous). Protium aguilarii also has usually shorter (non-basal) leafl ets than P. costaricense (6.7-13.2 vs. 10.5-17.5 cm), and glabrous fruits (vs. minutely pubescent with scattered trichomes), with a stipitate base, the stipe ca. 0.2 cm long (vs. sessile or with stipitate ca. 0.1 cm long). Additionally, P. aguilarii diff ers from P. costaricense by its smooth (vs. rugose) pyrene. In Costa Rica, others species with glabrous pistils or pistillodes are P. aracouchini Marchand, P. hammelii (described here), P. panamense (Rose) I. M. Johnst., and P. ravenii D. M. Porter. Unlike P. aguilarii, these species have nearly glabrous leaves and other vegetative parts. Protium aguilarii also shares some similarities with the South American P. pilosissimum including short infl orescences and pubescent leafl ets but it differs by its pubescent pistil or pistillode and fruit (vs. glabrous in P. aguilarii).
Habitat and distribution. Th is species is known so far only from wet forest on the Caribbean slope of Nicaragua and Costa Rica. It occurs mainly between 10 and 200 m in elevation, although some collections were made between 300 and 700 m. In Costa Rica, this species is common in the Sarapiquí region, where it seems to prefer alluvial soils on fl at or relatively fl at ground, sometimes on river banks. In this area, Protium hammelii grows sympatrically with the following species: Phenology. In Nicaragua, Protium hammelii has been collected with fruits in January, February, from May to July, and in October, but never in fl ower. In Costa Rica, it has been collected with staminate fl owers in January, February, April, and December; pistillate fl owers in January and February; and fruits in January, March, April, June, from August to October, and in December.
Etymology. Th e specifi c epithet honors Barry E. Hammel, curator at the Missouri Botanical Garden and co-editor of the Manual de Plantas de Costa Rica, in recognition of his extensive work on the Costa Rican fl ora, as well as his personal support and motivation.
Fruit dispersal by birds and mammals has been reported at the La Selva Biological Station for P. panamense (Vargas 2000), but the observation likely corresponds to P. hammelii.
Additional  Basionym: Trichilia brenesii Standl. Publ. Field Mus. Nat. Hist., Bot. Ser. 18: 583. 1937   Discussion. In the course of examining material identifi ed as Protium costaricense, a notable number of collections from Costa Rica, mainly from 640-1500 m elevation in the Cordilleras de Guanacaste, de Tilarán and Central, were identifi ed that diff ered from the rest. Th is material has twigs and leafl ets with inconspicuous pubescence on the abaxial side; leaves with more numerous and usually narrower leafl ets; and longer infl orescences and infructescences. Protium costaricense, as interpreted here, is a species of the lowlands of the Caribbean slope in Nicaragua, Costa Rica, and Panama, while the other collections represent a distinct montane taxon. An appropriate name already exists, and had been applied to some material collected in the Costa Rican cordilleras: Trichilia brenesii Standl. (1937: 583). Th erefore, a new combination is proposed here, transferring T. brenesii to Protium.
Th e fi rst known collection of Protium brenesii was made by Alberto M. Brenes  in the mountains near San Ramón, Alajuela Province, Costa Rica, in May 1923 (Brenes 19953). Th is species is similar in some aspects to P. costaricense, with which it has been confused for more than 90 years. Th ese two taxa share the following morphological characteristics: twigs and leaves with dense pubescence; entire leafl ets; 4(5)-merous fl owers with pubescent petals, pistil, and pistillode; and rugose pyrene. Th e leafl ets and fruits of the two species are also more or less similar in shape and size, In view of the long history of confusion involving Protium brenesii and P. costaricense, the following information is provided to clarify some important parameters of the latter species, as it is here interpreted: Habitat and distribution. Protium costaricense it is known from wet forests on the Caribbean slopes of Nicaragua (Atlántico Sur and Río San Juan Departments), Panama (Colón and Panamá Provinces), and Costa Rica. In Costa Rica, it is known from throughout the Caribbean coastal plain in Alajuela and Limón Provinces. It grows in primary forest and along river or forest edges, from 0 to 200 m in elevation (reportedly up to 500 m, according to the label of the type). Phenology. Collected with staminate fl owers in February and June; pistillate fl owers in February, July, and August; and fruits in January and from June to December.
Common name. In Nicaragua, this species is known as alcanfor (A. Laguna 73; R. Rueda et al. 5338). In Costa Rica and Panama, it goes by copal, chutra, kerosín and alcanfor (Condit et al. 2011