The Eke silversword, Argyroxiphium caliginis, is a rosette plant
endemic to the summit bogs of Eke Crater and Puu Kukui, West Maui, Hawaii.
On 2 November 1985, a belt transect across Eke Crater was used to estimate the
population of silverswords on the summit bog. Total population of the Eke
silversword on Eke Crater was estimated to be about 76,000 plants. Although the
plant has been described as a branching shrub that reproduces vegetatively, the
majority of the individuals in the sampled population of the Eke silversword on
Eke Crater were unbranched, monocarpic plants that appeared to reproduce by
seed

Powell, Elizabeth Ann

Pacific Science

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Pacific Science (1992), vol. 46, no . 3: 308-314© 1992 by University of Hawaii Press. All rights reservedPopulation Size and Frequency of Branching in the Eke Silversword,Argyroxiphium caliginis (Asteraceae), on Eke Crater, West Maui, Hawaii!ELIZABETH ANN POWELL2ABSTRACT: The Eke silversword, Argyroxiphium caliginis, is a rosette plantendemic to the summit bogs of Eke Crater and Puu Kukui, West Maui, Hawaii .On 2 November 1985, a belt transect across Eke Crater was used to estimate thepopulation of silverswords on the summit bog. Total population of the Ekesilversword on Eke Crater was estimated to be about 76,000 plants. Although theplant has been described as a branching shrub that reproduces vegetatively, themajority of the individuals in the sampled population of the Eke silversword onEke Crater were unbranched, monocarpic plants that appeared to reproduce byseed.THE EKE SILVERSWORD (Argyroxiphium calig-inis Forbes) is a rosette plant endemic to thesummit bogs and ridges of Eke Crater (1360m elevation) and Puu Kukui (1600 m) of WestMaui , Hawaii (Figure 1). The Eke silverswordis one of five extant species in the Hawaiiangenus Argyroxiphium (family Asteraceae, sub-tribe Madiinae). All members of the genus areendemic to Hawaii .The Eke silversword has been frequentlydescribed as a branching, dwarf shrub (Keck1936, Degener 1937, Neal 1965, Carlquist1974, Carr 1985, 1990). Degener (1930) de-scribed the growth habit of the Eke silver-sword as "creeping profusely over the groundand progressively dying back at the base,thus isolating the branches into independentplants." Carlquist (1974, 1980)suggested thatthe Eke silversword on Puu Kukui rarelyflowered and depended on branching for re-production. However, Forbes (1920), in hisdescription of the species, did not describe theEke silversword as a branching plant, butstated simply, "The plant proves to be aI This study was partially funded by a fellowship fromthe National Wildlife Federation. Manuscript accepted30 September 1991.2 Department of Botany , University of Hawaii atManoa, Honolulu, Hawaii 96822. Corresponding ad-dress: P. O. Box 61872, Boulder City, Nevada 89006-1872.different species from that found on either the .uplands of the island of Hawaii or of EastMaui. It differs from the other describedspecies in its much smaller size."Monocarpic silverswords live for manyyears as a vegetative single-stemmed rosetteand die after a single episode of flowering andsubsequent seed set. Branching is extremelyrare in the Haleakala silversword (A . mac-rocephalum Gray) (pers . obs.), occurs in lessthan 8% of the plants in a population ofthe Ka'u silversword (A. kauense (Rock andNeal) Degener and Degener) in the UpperWaiakea Forest Reserve on the island ofHawaii (unpublished data), and is present inabout 26% of the remnant naturally occur-ring population of the Mauna Kea silversword(A. sandwicense De Candolle) (Powell 1992).Therefore, the habit described by Degener(1930) for the Eke silversword is unusual forsilverswords. No other silversword specieshas been reported as capable of vegetativereproduction. However, the greensword(A . grayanum (Hillebrand) Degener) may becapable of vegetative reproduction in nature(G . Carr, pers. comm.).The purpose of this paper is to present anestimate of the population size, frequency ofbranching, and mode of reproduction of theEke silversword on the summit bog of EkeCrater.308The Eke Silversword-PowELLFIGURE I. A flowering Eke silversword on the summit bog of Eke Crater, West Maui , Hawaii .309310Study SiteEke Crater is an extinct volcanic dome witheroded sides and gently concave summit. Thesummit bog is underlain by a clay hardpanover a compressed lava core and is character-ized by numerous pits and open water ponds.The vegetation of the summit bog, whichconsists primarily of grasses , sedges, and low-growing shrubs, was in a pristine state at thetime of this study: Alien plants were absentand the vegetation appeared not to have beendisturbed by humans or feral animals. Thesummit of Eke Crater has been designated aNatural Area Reserve by the State of HawaiiDepartment of Land and Natural Resources.METHODSOn 2 November 1985, a 2 m x 360 m belttransect was extended in IO-m intervals fromthe north rim of Eke Crater across the centerof the summit to the edge of the south rim.The number of silversword plants, the rosettediameter of each plant, and the number ofrosette branches for each plant in the transectwere recorded. The transect covered only flatand gently sloping surfaces and did not in-clude pits. Less than 25 m2 of the transect wasopen water ponds.The number of flowering silverswords onthe summit of Eke Crater was estimated bycounting the number of flowering plants en-countered and in view during a 5-hr walkaround the perimeter of the summit bog. Therosette diameter and inflorescence height weremeasured on 81 flowering individuals, and thenumber of flowering stalks from previousflowering seasons that were encountered inthe walk was recorded. The height of theinflorescence from the ground surface wasmeasured for 39 flowering silverswords thathad fully elongated inflorescences.The area of Eke Crater was determined byplanimeter from a I : 24,000, 7.5-min. seriestopographic map published by the U.S. Geo-logical Survey. However, because the surfaceof the summit is not flat, but concave withnumerous pits , the planimeter reading for thesummit is an underestimate of the total sur-face area of the summit of Eke Crater.PACIFIC SCIENCE, Volume 46, July 1992RESULTSThe belt transect covered 720 m2 and rep-resented 0.005% (1/189) of the area of thesummit of Eke (13.6 ha), as determined byplanimeter. A total of 404 individual plants,of which three were in flower, occurred withinthe belt transect. If one assumes that thedensity of silverswords within the transect(0.56 plants per m") is the same as the densityof silverswords on the summit of Eke Crater,then the total population is estimated as thenumber of silverswords found in the transect(404) times the number of possible transectareas on the summit of Eke (189), or about76,000 silverswords.The distribution of rosette diameters of thesampled silversword population showed areverse J curve typical of expanding popula-tions (Figure 2). Forty-eight percent of theplants within the transect were < 10 cm indiam. There were, however, few seedlings < 3em in diam. It is possible that the silverswordsin this bog grow more rapidly than 1 or 2 emper year. If so, seedlings that resulted from theseed crop of 1984would have been larger than2 em by the time of this census in 1985. It isalso possible that seedling recruitment occursirregularly and that few seedlings were re-cruited in 1984.Sixty-nine of the 404 silverswords (17%)within the transect had multiple rosettes andwere considered branched; the remaining 335had only one rosette and were unbranched(monocarpic). Of the branched individuals,33% (n = 23) had two rosettes, 17% (n = 12)had three rosettes, and 14% (n = 10)had> 10rosettes. The maximum number of rosettes onany silversword plant in the transect was 36.Branched silverswords had several shootsthat terminated in rosettes radiating from acentral point on the aboveground shoot of theplant (Figure 3). The radiating shoots did notextend farther than about 20 em from thecentral shoot. In only one case was a radiatingshoot found to be rooted in the soil and theconnection between it and the parent shootbroken. Although no silverswords were exca-vated to make these determinations, no con-nections between plants were obvious in thesurface layers ofvegetation, nor were connec-The Eke Silversword- PoWELL 311PlIAJr Jr J~~ ~~ IAIAPlIA~ IA l/l40~ 30z~D...l..L.o 20D:::WCD2~z 10oo 10 20 30ROSETTE DIAMETER (em)40 50FIGURE 2. Distribution ofrosette diameters of thesampled silversword population on Eke Crater. Graph does notinclude two plants: one had a rosettediameter of61 em andtheother had a rosette diameter of84 em.tions between silverswords fou nd by gentlyprobing the vegeta tion to the soil surface inareas between plants . It is, however, possiblethat mo re connections existed than were en-countered by these methods.About 200 silverswords were in flower orbeginning to come into flower on the summitbog on 2 November 1985. Of the 81 floweringplants measured for inflorescence height, 39plants (48%) had fully elongated inflores-cences; the remainder (42 plants) had por-tions of the inflorescence in bud. The rosettediameter of the 81 flowering silverswordsranged from 15 to 44 em. The mea n diameterwas 27.0 em (n = 81, SD = 5.5) (Figure 4).The height of inflorescences ranged from29 to 81 em. The mea n inflorescence heightwas 51.8 em. Only 22 flowering stalksfrom previous flowering seasons were found .These stalks were fragi le and partially decom-posed.DISCUSSIONThe estimated population of about 76,000Eke silversword plants on Eke Crater waslarge r than the total estimated population ofany other species of silversword. The esti-mated population of the Haleakala silver-sword was about 50,000 plants in 1986 (Loopeand Crive llone 1986). The Haleakala silver-sword has suffered disturbance from humansand feral goats. The Mauna Kea silverswo rd,a federally listed endangered species, has beenreduced to a naturally occurring populationsize ofless than 40 individuals from a popula-tion that probably ranged over the alpine andsubalpine slopes of Mauna Kea before theintroduction of goats and sheep to HawaiiIsland (Powell 1992). The largest Ka'u silver-sword populat ion, which is located on Kahu-ku Ranch, Hawaii Island, has declined rapidlyfrom a "magnificent colony" of"several thou-312 PACI FIC SCIENCE, Volume 46, Ju ly 1992FI GURE 3. A branched Eke silversword on Eke Crate r.sand plants" in 1974 (Degener et al. 1976) toan estimated population size of less than 2000individuals in 1984 (unp ub lished data). Thisspecies has suffered grea tly from browsing bymo uflon sheep and has been pr op osed forlisting as an endangered species (U .S. Fishand Wildlife Service 1990).Althou gh the Eke silversword has repeat-edly been descr ibed as a branching or creepingshrub (Degener 1937, Neal 1965, Carr 1985),on ly 17% of the sampled po pulat ion on EkeCrater was found to be branched. Th e major-ity of the sampled population consisted ofmonocarpic, unbranched plants. This resultdoes not support the description of the Ekesilversword as a creeping shrub that repro-duces vegetatively. The freq uency of branch-ing observed for the Eke silversword on EkeCrater is less tha n the frequency of branchin gobse rved for the natu rally occurring popula-tion of the Mauna Kea silversword, which isconsidered primarily monocarpic .Carlquist (1974, 1980) suggested that theEke silversword on Puu Kukui rarely floweredand, the refore, depended on branching forreproduction. Thi s did not appear to be thecase on Eke Crater. Becau se few branc hin gsilverswords were encountered, numerous un-attach ed seedlings were found , and numerousplants were in flower, I conclude that the Ekesilversword reproduces primarily by seed onEke Crater.It is unknow n whet her the level of floweringobserved in 1985 (about 200 plants) was highor low compared to that of other floweringseasons. No other flowering censuses havebeen reported for the Eke silversword duringpeak flowering periods. Becau se old floweri ngstalks decom pose rapi dly, it was impossible toassess the level of flowering in previous years.Th e vegeta tion of Eke Cr ater was in apristine condition in 1985. The high density ofsilverswords on Eke Crater (about 5600 silver-swords per ha) suggests that other silverswordThe Eke Silversword -s-Powm.i, 31310 ,..--- - - - - - - - - - - - - - - - - - - ---,454020 25 30 35ROSEnE DIAMETER (em)15642O +----J~...1..>o...I.:~Lf'_"_':u.....>..t~~~~~~~..:LT_l---n~----CI...J.....-.I::>...'l..j108(f)I-Z:50....l')Z0:::W5o...Ju,u,o0:::Wrn2~zF IGUR E 4. Distribution of rosette diam eters of 8I flowering plants on Eke Cra ter on 2 November 1985.species may have been very numerous, andhad high population densities, before distur-bance by humans and feral animals.Although the Eke silversword populationappeared to be large and to be reproducing in1985, the silversword is threatened by fera lpigs (Gagne 1987). Where fera l pigs havegained access to pristine bog hab ita ts in Ha-waii, the native vegetation has declined rap-idly and alien weeds have replaced the nativevegetation (Medeiros et aI., in press) . UnlessEke Cr ater is completely protected from feralpigs, the Eke silversword will probabl y suffera rapid and drastic reduction of populationsize.ACKNOWLEDGMENTSI thank Lani Stemmermann, Betsy Gagne,Tom Hauptman , James Jacobi, and LawrenceWalker for their help and suppor t with differ-ent phases of this study.LITERATURE CITEDCARLQUIST, SHERWIN. 1974. Island biology.Columbia Uni versit y Press, New York.---. 1980. Hawaii: A natural history, 2ded. SB Printers, Inc ., Honolu lu.CARR, GERALD D . 1985. Monograph of theHawaiian Madiinae (Astera ceae): Argyroxi-phium, Dubautia, and Wilkesia . Allertonia4: 1-1 23.---. 1990. Argyroxiphium DC Silversword.Pages 258-262 in Warren L. Wagner, Der-ral R. Herbst , and S. H . Sohmer. Manualof the flowering plants of Hawai' i. Vol. I.Bishop Mus. Spec. Publ. 83. Uni versit y ofHawaii Press, Honolulu.DEGENER, OTTO. 1930. Plants of Hawaii Na-tional Pa rk illustrative of plants and cus-toms of the south seas . Braun-Brumfield,Inc., Ann Arbor.---. 1937. Argyroxiphium caligini. In Flo -ra Hawaiiensis. Family 344: Arg yroxi-phium. Honolulu.314DEGENER, OTTO, I. D EGENER, K. SUNADA, andA. SUNADA. 1976. Argyroxiphium Kauense,the Kau silversword. Phytologia 33: 173-177.FORBES, C. N. 1920. New Hawaiian plants.Occas. Pap. Bernice Pauahi Bishop Mus.7 :38-40.GAGNE, WAYNE C. 1987.Conservation corner.Newsl. Hawai i. Bot. Soc. 26 : 10-11.KECK, D AVID D . 1936. The Hawaiian silver-swords : Systematics, affinities, and phyto-geographic problems of the genus Argy-roxiphium. Occas. Pap. Bernice PauahiBishop Mus. II (19): 3-38.LOOPE, LLOYD L. , and CARMELLE F . CRIVEL-LONE. 1986. Status of the silversword inHaleakala National Park: Past and pres-ent. Cooperative National Park ResourcesStudies Unit Technica l Report 58. Univer-sity of H awaii at Manoa, Honolulu.PACIFIC SCIENCE, Volume 46, July 1992MEDEIROS, ARTHUR c., LLOYD L. LOOPE, andBETSY H. GAGNE. In press. D egradation ofvegetation in two montane bogs of Hale-akala National Park. Cooperative N ationalPark Re sources Studies Unit TechnicalReport. University of Hawaii at Manoa,Honolulu.N EAL, M ARIE C. 1965. In gardens of Hawaii .Bernice P. Bishop Mus. Spec. Pub!. 50.POWELL, ELIZABETH A. 1992. Life history,reproductive biology, and conservation ofthe Mauna Kea silversword, Argyroxiphiumsandwicense D C (Asteraceae), an endan-gered plant of Hawaii . Ph .D. diss. Univer-sity of Hawaii .U.S. FISH AND WILDLIFE SERVICE. 1990.Endangered and threatened wildlife andplants; proposed endangered status forArgyrox iphium kauense (Ka'u silversword).Fed . Regi st. 55(151): 31860-31 864 (6August 1990).

Population Size and Frequency of Branching in the Eke Silversword, Argyrox iphium caliginis (Asteraceae), on Eke Crater, West Maui, Hawaii.

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Population Size and Frequency of Branching in the Eke Silversword, Argyrox iphium caliginis (Asteraceae), on Eke Crater, West Maui, Hawaii.

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