Rubiacearum Americanarum Magna Hama Pars XII. A New Species of Ixora (Ixoreae) from Panama

Abstract

terminal, cauliflorous, or ramiflorous. The fragrant flowers are homostylous and generally white, yellow, or red. In her excellent revision of Ixora in Africa, De Block (1998) also highlighted the petiole bases, which are articulated from the stems (at least in dried specimens) in Ixora, as a good character for recognition of this genus. This character is found in Neotropical Ixora species as well. Other Neotropical Rubiaceae genera have not yet been widely surveyed for this feature; articulated petiole bases are known in a few other paleotropical genera, of several different tribes. The inflorescence axes of Ixora are also usually articulated, often giving them a distinctive appearance when dry. The flowers of Ixora exhibit an adaptation for pollination that is more common in Rubiaceae of the Paleotropics than the Neotropics, called secondary pollen presentation. The flowers of Ixora species are protandrous, and the anthers in bud are held closely around the style and stigmatic arms. Rather than presenting their pollen directly to pollinators, the anthers release and transfer some or all of their pollen onto the upper part of the style and the non-receptive abaxial surfaces of the stigmatic arms. Then this transferred pollen is exposed to pollinators for some period of time on these structures; after this the stigmatic arms separate and the stigmatic surfaces become receptive. The inflorescences of Ixora are considered terminal, most often arising directly from the apices of the main stems but sometimes borne on short lateral stems produced in the leaf axils. These lateral stems are called short shoots bearing terminal inflorescences by De Block (1998). In some Neotropical species the stem portion of these short shoots may be reduced so that the inflorescences appear to be axillary (e.g., I. yavitensis Steyermark). The inflorescences of Ixora are usually regularly branched with the higher order axes as well developed as the axis from which they branch; this condition was called trichotomous by De Block (1998). The inflorescences may vary markedly among species of Ixora in their degree of expansion, from strongly congested, with the axes only ABSTRACT. The new species Ixora knappiae C. M. Taylor (Rubiaceae) from the San Blas region of Panama, described and illustrated here, is notable for its opposite, subsessile, basally rounded to cordate leaves.