Two new South American species of Croton ( Euphorbiaceae ) and their phylogenetic affinities by

Riina, R. & Berry, P.E. 2010. Two new South American species of Croton (Euphorbiaceae) and their phylogenetic affinities. Anales Jard. Bot. Madrid 67(1): 23-27. Two rarely collected species of Croton from South America are des cribed and illustrated. Croton chimboracensis P.E. Berry & Rii na is localized in western Andean Ecuador and is sister to Croton sect. Adenophyllum Griseb. Croton abonari Riina & P.E. Berry is known from a single location in Amazonian Brazil; it resembles both C. sampatik Müll. Arg. and members of Croton sect. Cuneati (G.L. Webster) Riina & P.E. Berry, but C. abonari can be easily distinguished from both groups by distinctive morpholo-


Introduction
As a result of recent and ongoing taxonomic and phylogenetic studies on Croton, our understanding of this large genus has increased substantially, especially in the Neotropics, where several new species have recently been des cribed by our network of collaborators (Secco & al., 2001(Secco & al., , 2005;;Riina & al., 2007;Steinmann & Martínez-Gordillo, 2007;Carneiro-Torres & al., in press;Caruzo & al., 2008;Cordeiro & al., 2008;Lima & Pirani, 2008;Medeiros & al., 2009;Van Ee & Berry, 2009;Rii na & al., 2010aRii na & al., , 2010b)), and several more are currently in preparation.These new findings will not substantially change the number of species in the megadiverse genus Croton, since other published names are being synonymized at roughly the same rate (Caruzo & Cordeiro, 2007;Lima & Pirani, 2008;Van Ee & Berry, 2009;Riina & al., 2010b;Carneiro-Torres & al., in press;Gomes & al., in press).In this paper we des cribe two new species from South America that appear to be rare based on the few collections known to date, but are clearly distinct from any known species.

Results and discussion
In the first molecular phylogeny of Croton by Berry & al. (2005), and in a later work (Cordeiro & al., 2008)
This new species has some characters in common with members of Croton sect.Cuneati (G.L. Webster) Riina & P.E.Berry, such as the sinus glands on the leaf margin, stellate-lepidote trichomes, and the inflorescences in terminal or subterminal, apical clusters.Croton abonari differs from other members of C. sect.Cuneati in the adaxial position of the acropetiolar glands, which are usually abaxial in all the species of the section, in the cuspidate leaf apex, and in the much less dense indumentum on leaves and branches.Only one species in C. sect.Cuneati is glabrous, C. malambo, but it is restricted to dry coastal vegetation of northwestern Venezuela and northern Colombia.Unfortunately, the specimens of C. abonari lack seeds, which are morphologically quite distinct in species of C. sect.Cuneati (Riina & al., 2010b).In addition, all lowland species of C. sect.Cuneati grow in riparian or flooded forests (except C. malambo), whereas C. abonari has been reported from low elevation terra firme forests.Croton abonari also resembles C. sampatik Müll.Arg., ano ther Amazonian tree species in the Sampatik clade sensu Riina & al. (2009), in features such as number of stamens (16), and the morphology and position of the petiolar glands.The two species differ in the type of marginal glands, which are stipitate in C. sampatik and sessile in C. abonari, and the leaf apex, which is cuspidate in C. abonari, and acute and not cuspidate in C. sampatik.Mature pistillate flo-wers, fruits and seeds, in addition to molecular data, will be needed to determine with confidence the phylogenetic position of C. abonari within the Neotropical members of Croton.

Habitat and distribution
Croton abonari is so far only known from the type locality in Amazonas State, Brazil, where it grows in terra firme forests (rainforests that are not inundated by flooded rivers).
, C. chimboracensis (which was listed as Croton sp."Ecuador 7618") appeared in a position sister to all sampled members of C. sect.Cascarilla Griseb.(Fig. 3), now recognized as C. sect.Adenophyllum Griseb.by van Ee & Berry (2010).Riina & al. (2009) identified the distal inflated lobes of the columella as a synapomorphy for this section (C.sect.Cascarilla in their work), but C. chimboracensis does not possess the characteristic inflated columella lobes of other members of the section, but more flattened lobes instead (Fig. 2D).Thus C. chimboracensis could repre-New South American Croton sent a novel section in the genus, but until we obtain a broader sampling of species in and around C. sect.Adenophyllum, we prefer to leave it unplaced as to section.The US sheet of Hitchcock 20386 was annotated by Leon Croizat in 1939 as C. ruizianus var.cordatus Müll.Arg., but that taxon belongs unambiguously to C. sect.Adenophyllum, with its shorter stature (0.5-1.5 m), smooth, inflated, 3-lobed columella, more numerous stamens (30-42), and stellateporrect trichomes.Based on van Ee & Berry (2010) we use the name C. sect.Adenophyllum Griseb.for what Webster (1993), Berry & al., (2005) and Riina & al. (2009) treated as C. sect.Cascarilla Griseb.

Fig. 3 .
Fig. 3. Maximum likelihood phylogram of combined ITS and trnL-trnF data, showing the phylogenetic position of Croton chimboracensis (bold) sister to all sampled members of C. sect.Adenophyllum.Numbers above branches are parsimony bootstrap percentages.The labels on the right (gray) refer to sections of Croton.Figure modified from Cordeiro & al. (2008) and reproduced here with permission from the Botanical Journal of the Linnean Society (Wiley-Blackwell).

Fig. 5 .
Fig. 5. Croton abonari: A, petiolar glands on a juvenile (left) and a mature leaf (right), adaxial leaf side; B, detail of the inflorescence (flowers in bud).Photos taken from the holotype.