Monograph of the Genus Isodendrion (Violaceae) 
Hawaiian Plant Studies 21^ 
Harold St. John^ 
INTRODUCTION 
History 
The taxonomic history of the genus Iso- 
dendrion is brief. It was described by Asa Gray 
in 1852, being based upon the three new 
species, L pyrifoUum, I. longifolium, and 1. 
lauri folium, collected by the United States 
Exploring Expedition on Oahu, Sandwich 
Islands. Later, Gray gave a fuller account of 
the same three species (1854: 92-96) and 
illustrated two of them (1856: Atlas, pi. 8-9). 
Horace Mann, Jr., and W. T. Brigham did 
not find any of the species during their ex- 
ploration in 1864 and 1865, and Mann’s ac- 
count in his incipient "Flora of the Hawaiian 
Islands" (1866: 121-122) followed the treat- 
ments by his professor, Asa Gray. 
Hillebrand (1888: 18-19) gave a good treat- 
ment, with a key and lengthy descriptions. 
The several more recent collections by him- 
self and his associates were all identified with 
the three species published earlier by Gray. 
Hillebrand added no other species. 
A fourth species, 1. subsessili folium, was dis- 
^ This is the twenty-first of a series of papers de- 
signed to present descriptions, revision, and records of 
Hawaiian plants. The preceding papers have been 
published in Bernice P. Bishop Mus., Occas. Papers 
10(4), 1933; 10(12), 1934; 11(14), 1935; 12(8), 1936; 
14(8), 1938; 15(1), 1939; 15(2), 1939; 15(22), 1940; 
15(28), 1940; 17(12), 1943; Calif. Acad. Sci., Proc. IV, 
25(16), 1946; Torrey Bot. Club, Bui. 72: 22-30, 1945; 
Lloydia 7: 265-274, 1944; Pacific Sci. 1(1): 5-20, 1947; 
Brittonia 6(4): 431-449, 1949; Gray Herb., Contrib. 
165: 39-42, 1947; Pacific Sci. 3(4): 296-301, 1949; 
Bernice P. Bishop Mus., Occas. Papers 20(6): 77-88, 
1950; and Pacific Sci. 6(1): 30-34, 1952. 
2 Department of Botany, University of Hawaii. 
Manuscript received December 5, 1951. 
covered and described by Heller (1897: 856- 
857, pi. LIV) from the island of Kauai. 
MacCaughey gave a summarized account 
of the Hawaiian Violaceae and included Iso- 
dendrion (1918: 9-11). He stated that his paper 
was "the first comprehensive account which 
has included all of the recorded species and 
varieties. It is based upon field work extend- 
ing over nearly ten years and contains new 
ecological material." However, this paper 
added nothing to the knowledge of Isoden- 
drion. It copied word for word, or with slight 
paraphrasing, the treatment given by Hille- 
brand (1888: 18-19). Although the paper by 
Heller is included in his bibliography, 
MacCaughey makes no mention or dispo- 
sition of Heller’s very distinct and well- 
described and illustrated species from Kauai, 
/. subsessili folium. 
Relationship 
Gray, in describing the genus (1852: 324, 
and 1854: 93), emphasized that the flowers 
were regular, both calyx and corolla, and the 
stamens are so illustrated, but with "the 
unilateral stigma, which, in a flower otherwise 
perfectly regular, vindicates the relationship 
with the genuine Violeae.'’ He also indicated 
the stamens as entirely separate, and '^desti- 
tute of any prolongation of the connective . . .” 
He concluded that it was a member of the 
section Alsodineae and related to Alsodeia, 
Paypayrola, and Pentaloba. 
Bentham and Hooker (1862: 115-119)? not 
having seen any specimens of the genus 
Isodendrion, obviously relied heavily on Gray’s 
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