On the Submersion of Dicraurus into Iresine (Amaranthaceae)

The two species of Dicraurus Hook. f. (Amaranthaceae) are shown to be more closely related to different species in Iresine L. than they are to one another. In addition, characters used to distinguish Dicraurus are more widespread within Iresine than was formerly thought, necessitating the merger of Dicraurus into Iresine. The two species as placed in Iresine are I. alternifolia S. Wats. and I. leptociada (Hook. f.) Henrickson & Sundberg. Complete descriptions and distribution maps of the two species


INTRODUCTION
The genus Dicraurus Hook.f., consisting of a single species, D. leptocladus Hook.f. (Fig. 1a), was separated from Iresine on the basis of four characteristics: sessile stigmas, subglobose seeds, broadly concave cotyledons, and alternate leaves (Bentham and Hooker 1880).The genus has been universally accepted from its inception [although Airy Shaw (1960) proposed Dicrairus as the correct spelling] and received a second species.D. alternifolius (Wats.)Uline & Bray, in 1896 (Fig. 19).Standley (1915), however, did express doubts as to the validity of its recognition as a distinct genus.Studies in connection with the Chihuahuan Desert Flora revealed that other taxa of Iresine occasionally have alternate leaves, similar styles and seeds, and would appear to fit into Dicraurus.This stimulated an intensive study of the character states found within Dicraurus and Iresine to evaluate the relationships of the two genera.These studies indicate that the two species of Dicraurus appear to be more closely related to different species groups within Iresine than to one another and that their unique characteristics could easily be accommodated within Iresine.
No modem, comprehensive systematic treatment exists for Iresine.Standley (1917) recognized 32 species in North America but several more occur in South America.Within the tribe Gomphreneae, Iresine is characterized by having flowers arranged in small spikelets usually borne in broad, much-branched panicles.Calyces are terete, i.e., not laterally compressed, of separate sepals.The paired stigmas are subulate, borne on a short style.The androecium consists of a short basal tube bearing five, membranous, tapering filaments, typically alternating with five smaller, membranous, glabrous to pubescent pseudostaminodia (Fig. lk, 2c).Anthers are oblong, monothecal, and biloculed (Fig. Ij).Species range from perennial, erect to scandent, herbs to shrubs or small trees (reported to 12 m tall) with opposite leaves and perfect or unisexual flowers with plants sometimes being polygamous or dioecious.They may be glabrous or be variously pubescent to woolly with a variety of uniseriate, multicellular, simple or variously branched, straight or variously bent, smooth or aculeate (i.e., prickled) hairs on stems, inflorescences and leaves.As in other members of the Gomphreneae, pistillate flowers develop a dense wool of multicellular hairs at the base of the calyx that aid in fruit dispersal.Fruit vary from subglobose with a thin, membranous pericarp and broadly oblong cotyledons to more lenticular, with a thicker, more brittle pericarp wall and narrower cotyledons.

RESULTS AND DISCUSSION
The two species of Dicraurus are dioecious, occasionally polygammo-dioecious shrubs and, except for the consistent (D. leptocladus) or occasional (D. altern ifolius) alternate leaves, are similar in almost all respects to the dioecious, shrubby, more strongly vestitured species of Iresine (species 16 to 24 in Standley, 1917).
In addition to the features noted above, Dicraurus and the dioecious, shrubby, more strongly vestitured Iresines are also similar in certain minor features of the calyx and androecium.In most of these species, pistillate calyces are consistently shorter than staminate calyces.Pistillate calyces also tend to have sepals of uniform size.In contrast, the outer two sepals of staminate calyces are usually broader and three-veined while the inner sepals are narrower and one-veined.In staminate flowers the subulate filaments alternate with erect to incurved, mostly papillate to pubescent pseudostaminodia from one eighth to one third the filament length.Pistillate flowers all have a shallow disklike or cuplike androecial remnant subtending, but free from, the ovary that has 10 small teeth, five opposite the sepals (the staminodia) terminating in small glandlike, rounded tips, and five alternate the sepals (the pseudostaminodia) without rounded tips.In all these species, seeds are subglobose, with thin, light brown pericarp walls and their embryos have broadly oblong cotyledons about 0.7 mm wide.
In contrast, the herbaceous, dioecious Iresines (which are in a state of taxonomic chaos) have pistillate and staminate calyces of equal size.Pistillate flowers have only a five-toothed androecial remnant (the five pseudostaminal teeth are not present), and seeds are more lenticular in shape, with brittle, hard pericarp walls and embryo cotyledons are much narrower.
It becomes apparent that when Hooker established Dicraurus, he was contrasting the seed and embryo characteristics of Dicraurus with those of the herbaceous, dioecious Iresines rather than the shrubby dioecious Iresines with which they are basically identical in seed and embryo structures.Hooker's statement that Dicraurus has sessile stigmas appears in error as the herbaceous, dioecious Iresines have much shorter styles than those of Dicraurus leptocladus.The only character used by Hooker that remains to distinguish Dicraurus from Iresine is that of alternate vs. opposite leaves.This was the only character used by Uline and Bray (1896) to justify the transfer ofthe second species (D. alternifolius) into the genus and it is the only character used by Schinz (1893), Standley (1917), and all subsequent authors in floristic treatments to distinguish Dicraurus from Iresine.
While Dicraurus leptocladus (Fig. la) consistently has alternate leaves, leaves of D. alternifolius (Fig. 19) tend to be alternate only in distal portions of the stems, with some specimens showing no alternate leaves or nodes, others a mixture of opposite, subopposite and alternate nodes.Alternate nodes also occur in other species of Iresine.Some herbarium specimens ofthe perfect-flowered, shrubby I. angusti/olia Euphr.exhibit all alternate nodes while in other specimens all nodes are opposite.A mixture of opposite and alternate nodes similar to that found in D. alterni/olius also occurs in I. rotundi/olia StandI.from Puebla and Oaxaca (Fig. 2k).Elsewhere in the Amaranthaceae, alternate leaves is an important character used to distinguish the tribes Celosieae and Amarantheae from other primarily opposite-leaved tribes (Bentham and Hooker 1880;Standley 1917).This character is apparently not so taxonomically important in Iresine and Dicraurus.In light of this the relationships of the two species of Dicraurus to species of Iresine, as well as to one another, need reevaluation.
Evidence bearing on this question comes from analysis of additional characters such as vestiture.Dicraurus and the dioecious, woody species of Iresine are quite variable in vestiture.Most Iresine species, as well as D. alterni/olius, have uniseriate, multicellular, usually basally bent or geniculate trichomes with distinct aculeate processes on their surfaces (Fig. 3b--d).The distal portions of the trichomes may be either straight, and the vestiture sericeous (D. alterni/olius-Fig.3b) or the trichomes may be variously bent or contorted forming a more villous vestiture (I.rotundi/olia-Fig.3d).Dicraurus leptocladus, in contrast, has appressed, equally two-branched, dolabriform, aculeate trichomes (Fig. 3a), a type otherwise not known in Iresine.Other species of Iresine, however, have branched trichomes.Iresine pringlei S. Wats.and I. stricta StandI.have stellately branched trichomes with subequal, usually nonaculeate radii (Fig. 3e).Trichomes of I. schaffneri S. Wats.are two-branched and aculeate but the branches are very unequal in length and one branch is typically distinctly forked or further branched (Fig. 3c).While there is no exact match of the distinctive, equally two-branched trichomes of D. leptocladus (Fig. 3a) in Iresine, Iresine has such a wide diversity of simple and branched trichomes that the distinctive trichomes of D. leptocladus could easily be accomodated with the variation found in Iresine.
Within Iresine, D. alterni/olia appears to be most similar to I. rotundi/olia (Fig. 2k-r).Both are dioecious shrubs of arid habitats.In both, vestiture consists of basally bent, aculeate hairs, though the hairs are often more crinkled in I. rotundi/olia (Fig. 3b, d).Both have relatively small, thick, occasionally alternate leaves with secondary veins slightly raised beneath.Iresine rotundi/olia, however, tends to have less-branched inflorescences with flowers clustered in reduced glomerules (Fig. 21) rather than in open panicles of pedunculate spikes.The reduced pseudostaminodia also tend to be lacking in male flowers of Iresine rotundi/olia (Fig. 2n), though this is not consistent.
Relationships of Dicraurus leptocladus in Iresine appear less obvious.In its consistently alternate leaves it has no equal in Iresine.In its two-branched hairs and more lance-ovate leaves it is most similar to I. schaffneri (Fig. 2a-j) a species found in the southern Chihuahuan Desert.This species, however, has larger, opposite leaves, unequally branched trichomes, longer styles, staminate flowers +q.Pistil showing style, stigmas, basal staminodial complex.-r.Androecial complex showing staminodi a (with spheroidal processes) alternating with glabrous pseudostaminodia.(Scale in a also holds for k; scale in b holds for all flowers in c, e-f, g-i, m-q; scale in j also holds for d , r.) with narrow, lanceoloid sterile pistillodia, and more aggregated inflorescences borne on very long peduncles (Fig. 2a-j).It agrees, however, with D. leptocladus in most other features and, of all known species of Iresine, shows the greatest similarity with D. leptocladus.In the character of green mid stripes on pistillate sepals, D. leptocladus approaches I. pringlei, a species with stellately branched trichomes.
It becomes apparent that Dicraurus, as now recognized, is intimately related to Iresine and cannot even be distinguished on the basis of alternate vs. opposite leaves as alternate leaves also occur in other species of Iresine.Most of the other characters found in Dicraurus also occur in Iresine, and while Dicraurus leptocladus has some unique characteristics, a number of equally unique characters occur in other species of Iresine.We believe recognition of Dicraurus as a distinct genus, based on these few autapomorphic characteristics, is unsupportable and, as the two constituent species appear to be more closely related to different species of Iresine than to each other, the genus as it now stands is polyphyletic and thus unacceptable.We therefore adopt the following nomenclature, including one new combination.
Iresine leptoclada can be distinguished from all other Iresines by its consistently alternate, lance-ovate to ovate, relatively small leaves, and its distinctive equally two-branched, aculeate, appressed trichomes.In habit it is also somewhat distinctive in having very slender, weak stems and it reaches its maximum heights only when growing among other shrubs.It is occasionally reported as trailing over other bushes.As in other dieoecious Iresines, pistillate flowers are smaller than staminate flowers.Unlike most other species, however, the pistillate sepals are uniform in width and tend to be thicker and slightly green along the midvein.Occasional plants have perfect flowers (e.g., G. C. Nealley s.n.).
Iresine alternifolia is characterized by its shrubby, divaricately branched habit, by its relatively small, ovate, hairy leaves that tend to be alternate on the upper stems and also tend to develop in axillary clusters and on distinct short-shoot spurs, and by its dioecy.Trichomes are unbranched, aculeate, mostly bent at the base-a type widespread in Iresine.
The species occurs in the Sonoran Desert region both in Sonora north of Guaymas and in south-central Baja California (Fig. 4) in mesic, northerly facing canyons in the volcanic Sierra Gigantea and on several islands in the Gulf of California from (25-)90-1200 m elevation.Flowering occurs from (September-)October until January with fruit persisting into February.