UNIVERSITY OF

ILLINOIS LIBRARY

AT URBAIMA CHAMPAIGN

^ ^-BIOLOGY

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i FIELDIANA The UbmrvoHh.

i Botany

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Published by Field Museum of Natural History 8t Urbana-Chamrjaign

Volume 38, No. 6 March 18, 1977

Revision of Oparanthus

(Compositae, Heliantheae, Coreopsidinae)

TOD F. STUESSY

RESEARCH ASSOCIATE

FIELD MUSEUM OF NATURAL HISTORY

AND

ASSOCIATE PROFESSOR OF BOTANY

OHIO STATE UNIVERSITY, COLUMBUS

The subtribe Petrobiinae of the Compositae, tribe Heliantheae,

as recognized by Carlquist ( 1957), contains two genera: Oparanthus

Sherff with two species in the South Pacific and Petrobium R. Br.

with one species in the Atlantic. During recent investigations on the

Petrobiinae as part of a re-evaluation of subtribal limits in the

Heliantheae (Stuessy, in press), the relationships between these

two genera have been examined, as well as affinities with genera of

other subtribes. These comparisons suggest that Oparanthus and

Petrobium are similar morphologically, and that they have a strong

relationship with genera of the subtribe Coreopsidinae, especially

Bidens L. In this paper the taxonomic history of Oparanthus is

sketched, a commentary is presented on generic and subtribal

relationships, and a taxonomic treatment is provided that includes

two species that are restricted to the Tubuai Islands.

TAXONOMIC HISTORY

The taxonomic history of Oparanthus begins with the description

of section Quadrimera of Chrysogonum L. in the subtribe Melam-

podiinae. Forest Brown (1935), in one of his papers on the flora of

southeastern Polynesia, described this new section of Chrysogonum

which contained three new species from Rapa and the Marquesas

Islands: C. album, C. coriaceum, and C. rapense. His rationale for

inclusion of these new taxa within the genus stemmed from two

Library of Congress Catalog No.: 76-58128

US ISSN 0015-0746

Publication 1251 63 BIOLOGY LIBRARY

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64 FIELDIANA: BOTANY, VOLUME 38

factors: the presence of sterile disc florets which has often been

considered the most important character of the subtribe Melam-

podiinae (Hoffmann, 1890; Stuessy, 1973), and the existence of a

diverse assemblage of taxa already in Chrysogonum that were

distributed over the Pacific basin from the Philippines to Australia

(Stuessy, ms. in prep.). These three new species differed from the

rest of Chrysogonum in having woody stems and four-merous disc

florets.

In a paper dealing with several genera of Compositae of south-

eastern Polynesia, Sherff (1937a) elevated section Quadrimera to

generic status as Oparanthus with the simultaneous description of

a new species, O. intermedius. He gave no reason for this hier-

archical change except to note that (p. 12): "They [the first and last

four cited specimens in his paper] had been determined by Dr. Elmer

D. Merrill as Chrysogonum rapense F. Br. but with the exclamation

in each case that they were ' neither Chrysogonum norMoonia. ' '

Oparanthus remained within the subtribe Melampodiinae until

Carlquist (1957) suggested that the genus belonged with the mono-

typic Petrobium in the subtribe Petrobiinae. It is this taxonomic

disposition that Oparanthus holds at the present time.

GENERIC AND SUBTRIBAL RELATIONSHIPS

Oparanthus is indeed similar to Petrobium. Both genera are

shrubs of island habitats with oval to ovate leaves, four-merous

disc florets, campanulate disc corollas, a two-awned pappus, and

phyllaries and paleae containing brown-orange longitudinal striae.

These features emphasize the close relationship of the two genera

as well as a strong affinity with the subtribe Coreopsidinae. The last

three characters, in fact, are diagnostic of this latter subtribe

(Stuessy, 1973).

As detailed elsewhere (Stuessy, in press), the Petrobiinae seem

unworthy of subtribal recognition. Petrobium and Oparanthus are

regarded as belonging to the subtribe Coreopsidinae because they

possess the diagnostic features mentioned above (Carlquist, 1966,

also has suggested that Oparanthus is related to the Coreopsidinae).

Due to their four-merous disc florets and oval to ovate leaves, how-

ever, the two genera are somewhat isolated from the other taxa of

the subtribe. These two characters are not unknown in the Coreop-

sidinae, however, as the former occurs in Moonia Arn. (Stuessy,

1975) and in some species of Coreopsis (Smith, 1972), and the latter

STUESSY: REVISION OF OPARANTHUS 65

is found in Ericentrodea Blake & Sherff and in some species of

Bidens (Sherff, 1937b).

Oparanthus not only seems to be related to Petrobium and to

belong clearly in the Coreopsidinae, but also the genus appears to be

somewhat close to Bidens. This relationship has been suggested

indirectly by E. E. Sherff, the well-known authority on Bidens,

even though he himself described Oparanthus as new. In 1934,

Degener and Sherff (in Sherff) first described Bidens hivoana from

Hiva Oa in the Marquesas Islands. In 1935 Forest Brown described

his three new species of Chrysogonum, including C. album, and

among the paratypes of this new species is listed the type collection

(Mumford & Adamson 469) of Bidens hivoana. When Sherff moved

Brown's species of Chrysogonum to Oparanthus in 1937a he trans-

ferred C. album without any comment upon possible ties with

Bidens, nor did he comment on any such relationship in his mono-

graph on Bidens in that same year (1937b, p. 81). Although Sherff

never mentioned the closeness of Oparanthus and Bidens, the fact

that he included B. hivoana in the latter genus, while at the same

time accepting a specimen of that taxon also as a species of Opar-

anthus, suggests a strong connection between the two genera.

Whether the two species of Oparanthus recognized here should be

moved into Bidens and with which species (in addition to B.

hivoana) their affinities might lie are questions that must be ex-

amined further. Although apparently no species of Bidens occur in

the Tubuai Islands, numerous species exist on other islands in the

Pacific (Sherff, 1937b; Carlquist,1966). Exactly how Petrobium of

St. Helena in the Atlantic relates to Bidens also needs to be studied

carefully.

TAXONOMIC TREATMENT

OPARANTHUS Sherff

Oparanthus Sherff, Occas. Papers B. P. Bishop Mus. 12(19):9. 1937. Lectotype

species Oparanthus rapensis (F. Br.) Sherff

Chrysogonum L. sect. Quadrimera F. Br. Bull. B. P. Bishop Mus. 130:341. 1935.

Lectotype species Chrysogonum rapense F. Br.

Shrubs or trees. Leaves opposite, oval to broadly ovate, coarse to leathery.

Capitula in cymose clusters. Receptacle convex. Involucre cupulate, biseriate;

phyllaries coriaceous, ovate, with brown-orange longitudinal striae. Ray florets

carpellate, fertile; ligules yellow to yellow-green with brown-orange longitudinal

striae; pappus of 2-3 stout awns without barbs. Disc florets hermaphroditic, sterile;

corollas yellow with brown-orange longitudinal striae; anthers brown, abaxially

66 FIELDIANA: BOTANY, VOLUME 38

ridged; style filiform; stigma undivided; ovary filiform; pappus absent or of 1-2

narrow awns. Paleae coriaceous. Chromosome number unknown.

KEY TO THE SPECIES

1. Leaves 0.3 mm. thick, coarse but not leathery, with secondary veins

spaced 7-10 mm. apart and with reticulate tertiaries; heads 4-6 mm. tall;

phyllaries 2-3 mm. long 1. O. rapensis

1. Leaves 1 mm. thick, very leathery, with secondary veins spaced 2-5 mm.

apart and with the tertiaries paralleling the secondaries; heads 9-12 mm.

tall; phyllaries 5-8 mm. long 2. O. coriaceus

1. Oparanthus rapensis (F. Br.) Sherff, Occas. Papers B. P.

Bishop Mus. 12(19): 11. 1937. Figures 1 and 4.

Chrysogonum rapense F. Br. Bull. B. P. Bishop Mus.

130:343. 1935. TYPE: FRENCH POLYNESIA: Tubuai

Islands, Rapa, Maitua, "on talus with other trees and

ferns" [from label], 180 m., 10 Oct. 1921, A. M. Stokes 337

(Holotype,BISH!).

Tree to 8 m. tall. Stems terete, somewhat swollen at the nodes, to 8 mm.

diam. on upper branches, wrinkled when dry, glabrous. Leaves with petioles

3-9.5 cm. long, 1-2 mm. diam., at the base slightly expanded; blades oval,

6.7-13.7 cm. long, 7-14.5 cm. wide, at apex rounded to mucronate, at base

rounded, with the margins entire, with both surfaces glabrous. Capitula 4-6

mm. tall, 5-8 mm. diam., subsessile or more often on peduncles to 1 cm. long.

Receptacle 1 mm. diam. Phyllaries 6-10, ovate, coriaceous, 3-4.5 mm. long,

1.5-2.5 mm. wide, at apex rounded, glabrous. Ray florets 5-8; ligules 1.8 mm.

long, deeply trifid; tube 1.5-2 mm. long, 0.3 mm. diam.; pappus of 2 awns to

1 mm. long; achenes flattened radially with a weak central adaxial carina

(sometimes absent), 3-4 mm. long, 2.5-3 mm. wide, glabrous. Disc florets 8-15;

throat of corolla narrowly campanulate, 0.5 mm. long, 0.5 mm. diam.; lobes

narrowly ovate, 1.3 mm. long, 0.5 mm. wide, with a central midvein; tube

1.6 mm. long, 0.3 mm. diam.; anthers brown, 1.3 mm. long, with apical appen-

dage tapered, with basal lobes obtuse; style 3 mm. long, 0.1 mm. diam.; ovary

slender, 2-3 mm. long, 0.3-0.5 mm. diam.; pappus of 0-2 awns to 1 mm. long.

Paleae lanceolate, 3 mm. long, 0.7 mm. wide.

Distribution. —Common in lower elevational forests and cliffs

( 50-300 m. ) on Rapa Island of French Polynesia.

Flowering Dates. —Usually flowering in July, rarely in October

and December.

Specimens Examined. -FRENCH POLYNESIA: Tubuai

Islands: Rapa: wooded ravine, 8 Dec. 1934, Chapin 907 (A, NY);

SE slope of Mt. Ororangi, 6 July 1934, Fosberg 11413 (A, BISH,

GH); Mt. Tepiahu, 12 July 1934, Fosberg 11501 (BISH); valley

2/5 mile E of Ahurei, 1 July 1934, St. John & Fosberg 15264 (BISH,

STUESSY: REVISION OF OPARANTHUS

67

FIGS. 1-6. Illustrations of leaves (figs. 1-3) and diagrams of capitulescences (figs.

4-6) of Oparanthus rapensis (figs. 1, 4) [Fosberg 11501, BISH], O. rapensis X 0.

coriaceus ( = O. intermedius) (figs. 2, 5) [St. John, Maireau & Fosberg 15640, BISH],

and O. coriaceus (figs. 3, 6) [St. John & Maireau 15517, GH]. Figures 1-3, same scale.

The circles in Figures 4-6 represent individual heads.

GH, US); Maungaeae, E of Mangaoa Peak, 4 July 1934, St. John &

Maireau 15372 (BISH, GH); Peatuakaviri, W of Mt. Tautautu,

6 July 1934, St. John & Maireau 15401 (BISH, GH, US); Moron-

goto, 15 July 1921, Stokes & Brown 60 (BISH), 15 July 1921,

Stokes & Brown 76 (BISH); Pake, mountain side, 31 Oct. 1921,

Stokes & Brown 389 (BISH); dry cliffs above Maitua, 19 July

1934, Zimmerman s.n. (BISH).

2. Oparanthus coriaceus (F. Br.) Sherff, Occas. Papers B. P.

Bishop Mus. 12(19): 11. 1937. Figures 3 and 6.

Chrysogonum coriaceum F. Br. Bull. B. P. Bishop Mus.

68 FIELDIANA: BOTANY, VOLUME 38

130:344. 1935. TYPE: FRENCH POLYNESIA: Tubuai

Islands, Rapa, 1922, £. H. QuayleX (Holotype, BISH!).

Oparanthus intermedius Sherff, Occas. Papers B. P. Bishop

Mus. 12(19): 10. 1937. TYPE: FRENCH POLYNESIA: Tubuai

Islands, Rapa, Taratika, "east side of Mount Perahu, in thicket

on steep ridge," 500 m., 21 July 1934, H. St. John, J. Maireau &

F. R. Fosberg 15640 (Holotype, BISH!; isotype, GH!). Figures

2 and 5.

Shrub to 3 m. tall. Stems terete, swollen at the nodes, 1 cm. diam. on upper

branches, leathery when dry, glabrous. Leaves with petioles 2.5-4.5 cm. long,

1.5-2 mm. diam., at the base expanded; blades oval, 6.5-11 cm. long, 5-12 cm. wide,

at apex boat-shaped and obtuse to rounded, at base rounded, with the margin entire

to subserrulate, with both surfaces glabrous. Capitula 9-12 mm. tall, 6-10 mm.

diam., sessile or on peduncles to 3 mm. long. Receptacle 2 mm. diam. Phyllaries

ovate, coriaceous, 5-8 mm. long, 2-5 mm. wide, at apex obtuse, glabrous. Ray florets

5-8; ligules not observed; pappus of 2 or 3 stout awns 1.5-2 mm. long, with the

central awn the shortest; achenes flattened radially, with a strong central adaxial

carina, 3.6-4.2 mm. long, 1.7-2.9 mm. wide, glabrous. Disc florets 15-20; corollas not

observed; ovary 5 mm. long, 0.6 mm. diam. ; pappus of 0-3 main awns to 2 mm. long.

Paleae elliptic, 5 mm. long, 1.3 mm. wide.

Distribution.— Restricted to high elevations (350-500 m.) in

mossy forests in the island of Rapa in French Polynesia.

Flowering Date. —July.

Brown (1935) mentioned the absence of both discoid and radiate

corollas on his material of Oparanthus coriaceus, with the exception

of one immature 5-lobed disc corolla. Sherff (1937a) stated "ray

florets none" and noted the abundance of 4-lobed disc corollas. In

material at my disposal for study, including the collection (St. John

& Maireau 15517} cited by Sherff (1937a), I have seen neither

mature ray nor even immature disc corollas. Because the outer

series of achenes are clearly fertile and those in the center abortive,

I prefer to designate the outer, fertile achenes as belonging to ray

florets and those sterile ones of the center as disc florets. This same

morphological pattern prevails in O. rapensis, in which both radiate

and discoid corollas have been observed.

Oparanthus intermedius was described by Sherff in 1937a as

being morphologically intermediate (hence the specific epithet)

between O. rapensis and O. coriaceus in both floral and vegetative

features. This has been corroborated in the present study (figs. 1-6).

Only two collections of O. intermedius have been found: the type

collection, and a vegetative fragment in a mixed collection with

STUESSY: REVISION OF OPARANTHUS 69

O. coriaceus (Fosberg 11574, A). Because of the morphological

intermediacy of O. intermedius, its rarity, and its occurrence in one

population with O. coriaceus, one is tempted to regard the taxon as

a hybrid between O. rapensis and O. coriaceus. Additional con-

siderations support this hypothesis. The mountainous island of

Rapa is relatively small, being only 20 miles in circumference,

within which O. coriaceus is confined to elevations above 350 m. and

O. rapensis below 300 m. It is possible, therefore, that two (and only

two ) species of this genus have evolved within the small confines of

the island with O. coriaceus having speciated in isolation at higher

elevations from a founder population of the more wide-spread

O. rapensis. Recent disturbances, either natural or man-induced,

may have facilitated intermixing and resultant interspecific

hybridization.

Specimens Examined. —FRENCH POLYNESIA: Tubuai Is-

lands: Rapa: Mitiperu, dense damp woods, 18 July 1934, Fosberg

11574 (A [in part], BISH); Kaimaru, S ridge of Mt. Perahu, thicket

on steep mossy ridge, 13 July 1934, St. John & Maireau 15517

(BISH,GH).

EXCLUDED SPECIES

Oparanthus albus (F. Br.) Sherff, Occas. Papers B. P. Bishop Mus.

12(19): 12. 1937. Chrysogonum album F. Br. Bull. B. P. Bishop

Mus. 130:342. 1935. TYPE: FRENCH POLYNESIA:

Marquesas Islands, Hiva Oa, Feani, 850 m., 15 Dec. 1921,

F. & E. Brown 1088 (Holotype, BISH!). = Bidens hivoana

Degener & Sherff in Sherff, Bot. Gaz. 96: 143. 1934.

ACKNOWLEDGMENTS

Appreciation is expressed to the curators of the following her-

baria from which loans of specimens were made (acronyms after

Holmgren and Keuken, 1974): A, BISH, GH, NY, US; to the Na-

tional Science Foundation for support under Grant GB-37678; and

to my wife, Carol, for drafting the illustrations.

REFERENCES

BROWN, F. B. H.

1935. Flora of southeastern Polynesia-Ill. Dicotyledons. Bull. B. P. Bishop Mus.,

130, pp. 1-386 (cf. pp. 340-345).

70 FIELDIANA: BOTANY, VOLUME 38

CARLQUIST, S.

1957. The genus Fitchia (Compositae). Univ. Calif. Publ. Bot., 29, pp. 1-143.

1966. The biota of long-distance dispersal. II. Loss of dispersibility in Pacific

Compositae. Evolution, 20, pp. 30-48.

HOFFMANN, O.

1890. Heliantheae-Melampodinae, pp. 214-219. In Engler A. and K. Prantl, Die

natiirlichen Pflanzenfamilien, vol. 4(5), Leipzig.

HOLMGREN, P. K., and W. KEUKEN

1974. The herbaria of the world. Index Herbariorum. Part 1. Ed. 6. Regnum Veg.,

92, pp. 303-354.

SHERFF, E.E.

1934. Some new or otherwise noteworthy members of the families Labiate and

Compositae. Bot. Gaz., 96, pp. 136-153.

1937a. Some Compositae of southeastern Polynesia (Bidens, Coreopsis, Cosmos,

and Oparanthus). B. P. Bishop Mus. Occas. Papers, 12( 19), pp. 1-19.

1937b. The genus Bidens, part I. Field Mus. Nat. Hist. Publ. Bot., 16, pp. 1-346.

SMITH, E.B.

1972. Lobing of the disk flower corollas in North American Coreopsis (Com-

positae). Brittonia, 24, pp. 87-89.

STUESSY, T. F.

1973. A systematic review of the subtribe Melampodiinae (Compositae,

Heliantheae). Contrib. Gray Herb., 203, pp. 65-80.

1975. A revision of Moonia (Compositae, Heliantheae, Coreopsidinae). Brittonia,

27, pp. 97-102.

In press. A revised subtribal classification of the Heliantheae. In Harborne, J. B.

and V. H. Heywood, eds., The biology and chemistry of the Compositae.

Academic Press, N.Y.

UNIVERSITY OF ILLINOIS-URBANA