Arrabidaea chica

Caraballo-Ortiz, Marcos A., 2013, Rediscovery of Arrabidaea chica (Bignoniaceae) and Entada polystachya var. polyphylla (Fabaceae) in Puerto Rico, Phytotaxa 125 (1), pp. 53-58 : 53-54

Arrabidaea chica

Arrabidaea chica is a liana that can reach about 15 m in length with fragrant violet flowers produced in terminal panicles, and linear or narrowly-elliptical dehiscent capsules that produce many winged seeds ( Acevedo-Rodríguez 2005). This species is widely distributed in the continental Neotropics and is only documented in the Antilles from St. John, U.S. Virgin Islands ( Acevedo-Rodríguez 1996) and Puerto Rico ( Liogier & Martorell 2000, Acevedo-Rodríguez 2005). In Puerto Rico, A. chica is known from three collections made by Sintenis and Stahl at unspecified localities in the municipality of Bayamón in northern Puerto Rico (Urban 1903–1911, Fig. 1 ). Sintenis made a single collection of a fruiting individual of A. chica on 20 March 1885 on a limestone hill (Sintenis 1096, BM!, G!, GH!, K!, L!, W!), while the other two specimens were collected by Stahl from forests and thickets (Stahl 79 & 541). He considered these collections a new species and described them as Adenocalymna portoricensis Stahl (1888: 186) , which was latter placed in synonymy with A. chica (Urban 1903–1911, Acevedo-Rodríguez 2007). One of Stahl’s specimens was flowering on July 1886 (Stahl 541, L!), while the other (Stahl 79) has not yet been located. The specimens at B are no longer extant (Dr. Robert Vogt, pers. comm.). I have searched extant duplicates in over 25 herbaria in 11 countries, but the search has been unsuccessful. Apart from these three early collections, A. chica has not been recorded from Puerto Rico and it was thought that it was most likely extirpated ( Liogier & Martorell 2000, Acevedo-Rodríguez 2005).

In February 2007, during a botanical exploration of the “Monte de Santa Ana” limestone hills in Bayamón (18°24' N 66°08' W; 90 m a.s.l.; Fig. 1 ), a single individual of A. chica was found near the top of a limestone hill (Caraballo 1456 and 1480, UPR!). This individual was about 10 m long, sterile, shedding leaves, and growing on an exposed cliff scrambling over rocks and trees. The same plant was found fruiting in May 2009 (Caraballo 2855, UPR!). Further explorations to locate more individuals of the species on this and other limestone hills of the area have been fruitless. The vegetation at the site where A. chica was found is secondary and dominated by lianas, vines, and herbs. The surrounding vegetation is dominated by a developed limestone forest dominated by native trees such as Bursera simaruba (L.) Sarg. ( Burseraceae ), Guarea guidonia (L.) Sleumer ( Meliaceae ), and Sideroxylon portoricense Urb. (Sapotaceae) .

Besides Arrabidaea chica , the “Monte de Santa Ana” limestone hills are home to over thirty endangered, rare or remarkable species of the karstic region of northern Puerto Rico ( Table 1). Some of these are very rare and only known from one or a few individuals in the limestone hills of northeastern Puerto Rico. These include the trees Manilkara pleeana (Pierre) Cronq. (Sapotaceae) , Oxandra laurifolia (Sw.) A.Rich. (Annonaceae) and Coccothrinax barbadensis (Lodd. ex Mart.) Becc. (Arecaceae) , the endemic shrub Malpighia fucata Ker Gawl. (Malpighiaceae) and the vines Jacquemontia verticillata (L.) Urb. ( Convolvulaceae ) and Canavalia nitida (Cav.) Piper (Fabaceae-Faboideae). In contrast, some rare and endangered species maintain numerous populations in this area, such as the trees Erythrina eggersii Krukoff & Moldenke (Fabaceae-Faboideae) and Ottoschulzia rhodoxylon (Urb.) Urb. (Icacinaceae) . Interestingly, a nearby limestone hill holds a large population of the endangered plant Buxus vahlii Baill. (Buxaceae) , suggesting that not all limestone hills in this area share the same composition of rare species. These hills have served as a shelter for the native flora because their rugged topography made them unsuitable for agricultural purposes and as such they were not completely deforested during the intense agricultural period of the 18 th and 19 th centuries. The conservation of these limestone hills is crucial for the survival of many native species of plants and animals, particularly in highly populated and fragmented landscapes such as the metropolitan area of San Juan. At present, the limestone hill where A. chica was found is legally protected by the National Park Company of the Government of Puerto Rico as part of the Julio Enrique Monagas National Park. In addition, A. chica is listed as a critical element of the flora of Puerto Rico by the Department of Natural and Environmental Resources of The Commonwealth of Puerto Rico ( DNER 2008). Besides the legal protection, the successful conservation of A. chica in Puerto Rico is dependent on the specific preservation and propagation of the known individual. The main current threats to its survival are wild fires and vegetation clearance, particularly on the cliffs where rock climbing is practiced. Although vegetative propagation (through branch cuttings using a rooting hormone) has been successful, propagation by seeds has failed. The conservation of A. chica also has medical relevance, as the species has anti-inflammatory and wound-healing properties, among other benefits (e.g., Jorge et al. 2008).

Figures

FIGURE 1. Map of the island of Puerto Rico showing the localities where the lianas Arrabidaea chica (circle) and Entada polystachya var. polyphylla (triangle) were rediscovered. The historical localities where E. polystachya var. polyphylla was collected during the 19th Century includes the municipality of Fajardo (rhombus) and the area between the municipalities of Manatí and Vega Baja (square). All the historical records of A. chica are from unspecified localities within the municipality of Bayamón.