Arceuthobium abietinum Subspecies Wiensii , a New Subspecies of Fir Dwarf Mistletoe (Viscaceae) from Northern California and Southern Oregon

2009·6.8 MB·English

by  Robert L Mathiasen

Madrono, Vol. 56, No. 2, pp. 118-126, 2009
ARCEUTHOBIUM ABIETINUM SUBSPECIES WIENSII, A NEW SUBSPECIES OF
FIR DWARF MISTLETOE (VISCACEAE) FROM NORTHERN CALIFORNIA AND
SOUTHERN OREGON
Robert L. Mathiasen
School of Forestry, Northern Arizona University, Flagstaff, AZ 86011 USA
[email protected]
Carolyn M. Daugherty
Department of Geography, Planning, and Recreation, Northern Arizona University,
AZ USA
Flagstaff, 86011
Abstract
WedescribeArceuthobiumabietinumsubspecieswiensii(Wiens'dwarfmistletoe,Viscaceae), adwarf
mistletoe that severely parasitizes red fir and Brewer spruce in northwestern California and
southwestern Oregon. This classification is based on morphological and host range differences
between white fir dwarfmistletoe {Arceutlwbium abietinwn f. sp. concoloris), red fir dwarfmistletoe
{ArceutJwbium abietinum f. sp. magnificae), and Wien's dwarfmistletoe. Male and female plants of
Wiens' dwarf mistletoe were consistently smaller than those of both white fir and red fir dwarf
mistletoes, whose plants were about the same size. The shoot color of Wiens' dwarfmistletoe was
frequently green-brown or red-brown, while the shoot color ofwhite fir and red fir dwarfmistletoes
was typically yellow-green or yellow. Differences in host specificity also distinguish Wiens' dwarf
mistletoe from white and red fir dwarfmistletoes.
Resumen
Se describe Arceuthobium abietinum subespecie wiensii (muerdago enano de Wiens, Viscaceae), un
muerdago enano que parasita severamente a Abies magnifica y a Pieea breweriana en el noroeste de
CaliforniaysuroestedeOregon. Estaclasificacionsebasaendiferenciasmorfologicasydehospederos
entre el muerdago enano del oyamel bianco {Arceuthobium abietimim f. sp. concoloris), el del oyamel
rojo{Arceuthobiumabietinum f. sp. magnificae), yeldeWiens. Lasplantasmasculinasyfemeninasdel
muerdago enano de Wiens son consistentemente mas pequeiias que las del muerdago enano del
oyamelbiancoylasdeloyamelrojo,lascualessondetamanosimilarentresi. Elcolordelasramasdel
muerdago enano de Wiens fue frecuentemente cafe verdoso a cafe rojizo, mientras que el de los
muerdagos del oyamel bianco y del oyamel rojo tipicamente fue verde amarillo o amarillo.
Adicionalmente, el muerdago enano de Wiens se distingue de los otros dos por diferencias en la
especificidad de sus hospederos.
Key Words: Abies concolor, Abies magnifica, Arceuthobium, dwarfmistletoe, Picea breweriana.
Fir dwarf mistletoe {Arceuthobium abietinum Engelm. ex Munz f. sp. magnificae Hawksworth
Engelm. ex Munz) is a common parasite ofwhite & Wiens, which parasitizes red fir.
fir {Abies concolor (Gordon & Glend.) Hilde- Parmeter and Scharpf (1963) were the first to
brand; including var. lowicma (Gordon) A. report the extreme host specificity of fir dwarf
Murray), and red fir {Abiesmagnifica A. Murray; mistletoe populations based on cross inoculation
including var. shastensis Lemmon) in the Sierra studies and their field observations in mixed red
Nevada Mountains, Cascade Range, and the and white fir stands in the Sierra Nevada
Klamath and Siskiyou Mountains of northwest- Mountains. Although Hawksworth and Wiens
ern CaHfornia and southwestern Oregon (Hawks- (1972, 1996) did not find morphological or
worth and Wiens 1972, 1993, 1996). Fir dwarf phenological differences between the fir dwarf
mistletoe populations that parasitize white fir in mistletoe populations parasitizing white and red
the Sierra Nevada Mountains do not infect red fir, their field observations in the Sierra Nevada
fir, while the fir dwarf mistletoe populations Mountains confirmed the host specificity report-
infecting red fir do not infect white fir, yet they ed by Parmeter and Scharpf. Due to the
are all morphologically similar. Recognizing this economic impact that A. abietinum has on true
distinction, Hawksworth and Wiens (1972, 1996) firs in California, Hawksworth and Wiens (1972,
named two special forms of A. abietinum: A. 1996) argued that since the host affinities of the
abietinum Engelm. ex Munz formae speciales two fir dwarf mistletoes were so distinct, they
concoloris Hawksworth & Wiens, which parasit- deserved taxonomic recognition and designated
izes white fir, and Arceuthobium abietinum them as formae speciales in accordance with
2009] MATHIASEN AND DAUGHERTY: ARCEUTHOBIUM ABIETINUM SUBSP. WIENSII 119
recommendation 4B ofthe International Code of morphological, phenological, and host suscepti-
Botanical Nomenclature. bility studies of the populations of dwarf
Although Nickrent et al. (2004) suggested a mistletoes parasitizing true firs and Brewerspruce
taxonomic classification that treats A. ahietinwn in northern California and southwestern Oregon
under A. campylopodum Engelm. based primarily in 1998. Our morphometric analyses and data on
on molecular data, we reject this alternative host susceptibility differences support the de-
classification and adopt the taxonomic treatment scription of a new subspecies of fir dwarf
for Arceiithobium of Hawksworth and Wiens mistletoe.
(1972, 1996) which distinguishes A. ahictinum Arceuthobium abietinum Engelm. ex Munz subsp.
fhorsotmrAa.ngceujduipffyelroepnocdeswubeutsiwnegenmotrhpehsoelsopgeiccieasl.aWned Wwiieennssii'Mdawtahrifasmiesntl&etoCe..—DauTgyhpeer:tyU,SAsu,bsCpa.linfoovr.-
also agree with Hawksworth and Wiens' (1996)
nia, Siskiyou Co., 41 49'21"N, 123 28'05"W.
classification of the dwarf mistletoe populations
Elev. 1820 m. Klamath National Forest, Baldy
that parasitize Pacific silver fir {Abies amahilis Mountain, 18.2 km west of Indian Creek on
DReohudgelra)s ienxOJr.eFgoornbeasn)danWdasnhoibnlgetofinr a{sA.hpermolcoecrka ofonresPtirede.a17brNe1w1er(Diaonoal,itt8leACurge.e,k r2d0.0),8.parRa.sitLi.c
dwarf mistletoe {Arceuthohium tsugense (Ro- Mathiasen and CM. Daugherty 0823 (holo-
send.) G. N. Jones) although we have determined type: ASC; isotypes: JEPS, UNM, US).
that two subspecies of hemlock dwarf mistletoe
parasitize these true firs to different degrees Plantae 4-16 (9) cm altae; surculi prinicipales
s(uMbastpheicaiseesnofahnedmlDoacukgdhwearrtfymi2s0t0l5e,toe20t0h7a)t.ocTchuer mbamsi 2l-o6ngi(3s),m2mmdmiaml.at;isi;ntferruncotduissmtearttiuirsi6-42.72 m(1m4)
on Pacific silver and noble firs can be distin- longi, 3.0 mm latis; anthesis mense Julio Au-
guished from fir dwarf mistletoe by their gusto; fructus maturitas Septembri Octobri. In
differences in shoot color and their inability to Abies niagnifiea et Pieea breweriana parasiticae.
parasitize red fir (Hawksworth and Wiens 1996; Plants 3.8-16.1 cm in height (mean ca. 9 cm);
Mathiasen and Daugherty 2005, 2007). Further- basal diameter of dominant plants 1.8-5.8 mm
more, white fir dwarf mistletoe does not infect (mean 3.1 mm); third internode length 5.6
western hemlock (Tsuga heterophylla (Rafael) 27 mm (mean 14.0 mm) and 1.9 mm wide
Sargent) although this hemlock is frequently (Figs. 2 and 3); staminate plants primarily
associated with infected white firs in Oregon green-brown, but many red-brown; pistillate
and grand firs {Abies gram/is (Douglas ex D. plants primarily green-brown, but some red-
Don) Lindley) in Washington (Hawksworth and brown or, rarely, yellow-brown; staminate flow-
mm
Wiens 1996). ers 3 or 4-partite, flower diameter 2.0-3.8
mm
In 1996 we were shown a population ofdwarf (mean 2.8 mm); mature fruit length 3.1 5.0
mistletoe severely parasitizing red fir and Brewer (mean 4.2 mm) and 2.2-3.5 mm wide (mean
mm
spruce {Pieea brewericma Watson) by Dr. Gregg 3.0 mm)(Fig. 4). Seeds 1.9-2.9 long (mean
DeNitto, USDA Forest Service, which occurred 2.4 mm) and 0.9-1.5 mm wide (mean 1.1 mm).
near Baldy Mountain northwest ofHappy Camp, Phenology: Anthesis from early July through
California (Fig. 1, site 11). Although the dwarf late August with peaks in late July to early
mistletoe plants there resembled fir dwarfmistle- August; seed dispersal from early September to
toe, plants on both hosts were green-brown or mid October with peaks in late September to
red-brown instead of the typical yellow-green to early October.
yellow offir dwarfmistletoe in the Sierra Nevada Habit: Principally parasitic on Abies magnifiea
Mountains (Hawksworth and Wiens 1996). and Pieea breweriana. Occasionally parasitic on
Furthermore, the dwarf mistletoe occasionally Abies concolor and Abies lasioearpa (Hook.)
infected white fir indicating it was not Areeutho- Nutt. Rarely parasitic on Pinus niontieola Dou-
bium ahietinum f. sp. magnificae {sensu stricto). glas ex D. Don. The host susceptibiUty classi-
Our examination ofanother population ofdwarf fication used here and below is based on the
mistletoe parasitizing white fir and Brewer spruce system described in Hawksworth and Wiens
near Flat Top Mountain west of Grants Pass, (1996).
Oregon (Fig. 1, site 6) also showed the plants at Distribution: Wiens' dwarfmistletoe occurs in
this location were green-brown to red-brown, but northwestern California from South Fork Moun-
otherwise resembled fir dwarfmistletoe. The Flat tain (Trinity Co.) north through the Siskiyou and
Top Mountain population had been previously Klamath Mountains into southwestern Oregon
classified as A. abietinum f. sp. eoneoloris because on Flat Top Mountain (Josephine Co.)(Fig. 1).
white fir was also parasitized there (Hawksworth Elevational range is from ca 1500 m on South
et al. 1967; Hawksworth and Wiens 1972, 1996). Fork Mountain to as high as 2000 m on Baldy
Since the fir dwarf mistletoe on Baldy and Flat Mountain northwest ofHappy Camp, California.
Top Mountains infected both red and white firs, Representative specimens: Areeuthobiuni abie-
as well as Brewer spruce, we began intensive tinum subsp. wiensii Paratypes: [all citations
——
MADRONO
120 [Vol. 56
Fig. 1. Approximate locations ofpopulationssampled forArceuthobiumabietinum subsp. wiensii, A. abietinumf.
srpe—.prneusiegnntiffi.csape.annuidgnAi.fiacbaieeat—innducmlfo.sespd.ccirocnlceoslorreipsr.esOepnetnf.csipr.c—lceosncionldoirciast.eLpoocpautliaotniso:ns1—ofBisgubTsrpe.ewriednsNii,ofoTpreonutsqLuaakree;s
2—eastsideofSuttle Lk.; 3 17 km S ofSistersonrd—16;4 south bound—aryofCraterLake—Nat. Parkon Rte. 62;
B5ola1nkMmtnE—.;of1e0n—trJeatn.coeftGorJeoysbeapchkSrtdewaanrdt rStd.tPoarKke;ll6y L—kF.l;at11To—pBaMltdny.;Mt7n.S1t8evkemFoWrkofCrI.n;d8ianAClrteheokusoenMDtono.l;it9tle
Cr. rd; 12 Rock Creek Butte 41 km N—ofOrleans; 13 YellowJacket Ridge on trail to Chimn—ey Rock Lk.; 14
2E0tnkamSuNmmofitRtoeW.n3r6d;t1o7S—awSyoeurtsh BFaorr;k1M5tn.38kmkmNNofofEaRttWeo.n3L6k;.1i8n—Ru1s0skiamnWPeoafkSWtielwdaerrtneHsost; s1p6rinWSgsouotnhPFaorrkkCMrtene.k
rLda;ss1e9n—N1atk.mParkoofnBlRtaec.k4B4u;tt2e2—tra1i6lhkemad;S2o0f—n1or0thkmentranocfeMtcoCLlaosusdenoNnatR.teP.ar89k;o2n1R—t1e1. 8k9;m23—of17enktmraSncWe toof
2009] MATHIASEN AND DAUGHERTY: ARCEUTHOBIUM ABIETINUM SUBSP. WIENSII 121
cm
1
Fig. 2. Male plants ofArceuthobium abietinum subsp. wiensii in September.
based on Abies magnifica except as noted] USA. (ASC); same site, on Abies lowiana, Mathiasen
OREGON. Josephine Co.: Flat Top Mountain, 0333 {cr) (ASC); same site, 2007, Mathiasen 0746
on Picea brewericma, 2003, Mathiasen 0357 (o*) (9) (ASC); same site, on Picea breweriana,
(ASC); same site, 2007, Mathiasen 0741 {cr & Q) Mathiasen 0745 (9) (ASC); same site, 2008, on
(ASC); same site, on Abies lowiana, Mathiasen Picea breweriana, Mathiasen & Daugherty 0823
0742 (o- & 9) (ASC) (Fig. 1, site 6); Steve Creek, {cr & 9) (ASC) and Mathiasen & Daugherty 0833
on Picea breweriana, 2003, Mathiasen 0360 {cr & (9) (ASC); Etna Summit, 2008, Mathiasen 0830
9) (ASC) (Fig. 1, site 7); Althouse Mountain, {cr &9) (ASC) (Fig. 1, site 14); Trinity Co.: South
2003, Mathiasen 0336 (cr & 9) (ASC) (Fig. 1, site Fork Mountain, 2008, Mathiasen 0865 {cr & 9)
t8a)i.n,CA20L0I7,FOMRatNhIiAas.enSi0s7k4i3yo(ucrC&o.:9)B(oAlSaCn);Mosuanm-e (AASC)to(tFailg.o1f, s7itepo16p)u.lations of Arceuthobium
site, 2008, Mathiasen 0835 (9) (ASC) (Fig. 1, site abietinum subsp. wiensii were sampled from
9); Baldy Mountain, 1998, Mathiasen 9884 (o-) within its geographic range (Fig. 1). From each
(ASC) (Fig. 1, site 11); same site, on Abies population, 20 to 40 infections were collected and
lowiana, Mathiasen 9883 {Cf) (ASC); same site, the dominant shoot from each infection was used
on Picea breweriana, Mathiasen 9885 {cr) (ASC); for morphological measurements. For each pop-
same site, 2003, Mathiasen 0334 {cr) (ASC); same ulation, 10 or 20 male and female infections were
site, on Picea breweriana, Mathiasen 0332 {cr) collected.
W
Old Stat—ion on Rte. 44; 24—W13 km SE ofrd A21 on Rte. 44; 25—6 km ofMeadow Valley on road to Bucks
Lak—e; 26 WGrizzly Summit ofBucks Lake; 27—1 km E ofLyons C—r. TrailheWad; 28—Echo Summit on U.S. 50;
29 9 km ofCrane Flat on Tioga Pass rd, Yosemite Nat. Park; 30 16 km ofCrane Flat on Tioga Pass rd,
Yosemite Nat. Park; 31—10 km E ofFish Camp on rd 6S07; 32—11 km E ofFish Camp on rd 6S07.
[Vol. 56
Fig. 3. FemaleplantsofArceuthohiumahietinum subsp. wiensiiinNovember. Theseplantshavedevelopingfruits
that will be mature the following year.
cm
1
Fig. 4. Mature fruits ofArceuthohium ahietinum subsp. wiensii in October.
2009] MATHIASEN AND DAUGHERTY: ARCEUTHOBIUM ABIETINUM SUBSP. WIENSII 123
In order to make a comparison with the were green-brown, particularly at the northern
morphological characters of Arceuthobiuni abie- end of its geographic range, but none were red-
tinum f. sp. magnificae a total of6 populations of brown. The reddish-brown to nearly orange color
f. sp. magnificae were sampled from the central of the plants of subsp. wiensii is a distinctive
and northern Sierra Nevada Mountains (Fig. 1). character of this dwarfmistletoe.
From each population, 20 to 40 infections were Staminateflowersofsubsp. wiensiiwere smaller
collected and the dominant shoot from each insize(both 3 and4-merousflowers)thanthoseof
infection was used for morphological measure- f. sp. concoloris and f. sp. magnificae (Table 1).
ments. For each population, 10 or 20 male and The mean diameters of both 3- and 4-merous
female infections were collected. In addition, 20 flowers for subsp. wiensii were statistically differ-
populations of ArceutJwbium abietinwu f. sp. ent than those ofthe special forms. Hawksworth
concoloris were sampled throughout most of its and Wiens (1972, 1996) reported that staminate
geographic range (Fig. 1). Fromeach population, flower diameters ofA. abietinum (for both special
10 male and 10 female infections were collected forms) were2.5 mm, so thismust havebeen for 3-
and the dominant shoot from each infection was merous flowers because our measurements of 3-
used for morphological measurements. merous flower diameters averaged 2.6 and
mm
The dwarfmistletoe plant characters measured 2.7 for A. abietinum f. sp. concoloris and f.
were those used by Hawksworth and Wiens sp. magnificae, respectively. Hawksworth and
(1996) fortaxonomicclassification. The following Wiens did not report flower diameters for 4-
morphological characters were measured: height, merous flowers, but we found that the average
basal diameter, third internode length and width, diameter of 4-merous flowers was smaller for
and color of the tallest male and female shoot subsp. wiensii(3.2 mm) than for the special forms
from each infection collected; mature fruit length, (3.5 mm). Another character which typically is
width, and color; seed length, width and color; not infoiTnative, but was significantly different
staminate flower diameter; number, length and between subsp. wiensii and the special forms was
width of staminate perianth lobes; and anther the distance of the anther from the tip of the
mm
diameter and anther distance from the perianth perianth lobe. This distance averaged 0.4
lobe tip. Plants were measured within 24 hr after (range 0.2-0.7 mm) for the special forms, but
mm
collection and were measured using a digital averaged 0.6 for subsp. wiensii and some
caliper, a dissecting microscope with a microme- anthers were as much as one mm from the tip of
ter, or with a Bausch and Lomb 7X hand lens the perianth lobe. This character could often be
equipped with a micrometer. A minimum of 100 observed when comparing the anther location on
measurements or observations of color were perianth lobes between the special forms and
made for each character above. A one-way subsp. wiensii using a lOX hand lens.
analysis of variance (ANOVA, P < 0.05) was Fruits of Arceuthobium abietinum subsp. wien-
used to determine if there were statistical sii were smaller on average than those for both
differences between the means ofthe morpholog- special forms (Table 1), but the range in fruit
ical characters measured. length and width overlapped for all three taxa.
Plants of Arceuthobium abietinum f. sp. con- However, the mean length ofthe fruits of subsp.
colorisand f. sp. magnificaeweremorphologically wiensii was statistically different than the mean
similar as reported by Hawksworth and Wiens lengths of the special forms, but not the mean
(1972, 1996). Although several morphological width. Furthermore, the color offruits for subsp.
characters were similar between the special forms wiensii was green-brown to green while the color
of A. abietinum and A. abietinum subsp. niensii, of fruits for both special forms was consistently
there were several consistent morphological green. Seeds ofsubsp. wiensiiwere also smalleron
differences (Table 1). Male and female plants of average than those of the special forms, but the
subsp. wiensii were consistently smaller than differences were not statistically significant.
those of both f. sp. concoloris and magnificae, The principal hosts ofArceuthobium abietinum
whose plants were about the same size. Differ- subsp. wiensiiwere red fir and Brewer spruce, but
ences in plant height were not statistically it is most common on red fir. We presently know
different between the special forms of A. abieti- ofonly three locations where it occurs on Brewer
num, but the plant heights of subsp. wiensii were spruce; Flat Top Mountain and Steve Creek,
different than the plant heights of the special Josephine Co., Oregon and Baldy Mountain,
forms for both male and female plants. As noted Siskiyou Co., California. However, it severely
eadier, the color of plants of subsp. wiensii were parasitizes Brewer spruce at these locations, but
frequently green-brown or red-brown, while the only a few spruces are infected near Steve Creek
color of plants of f. sp. concoloris and f. sp. and the 2002 Biscuit Fire killed most of the
magnificae were typically yellow-green, or yellow severely infected spruce on Flat Top Mountain.
as described by Hawksworth and Wiens (1972, However, our observations on Flat Top Moun-
1996). However, occasionally the female plants, tain and those ofHawksworth et al. (1967) before
and rarely the male plants of f. sp. magnificae the Biscuit Fire indicated that many Brewer
MADRONO
124 [Vol. 56
Table 1. Morphological Measurement Results for White Fir Dwarf Mistletoe, Red Fir Dwarf
Mistletoe, and Wiens' Dwarf Mistletoe. Data are presented as means with range, and (sample size) below.
Means followed bydifferent letters in the same rowwere significantlydifferent (ANOVA, P < 0.05). Plant heights
in cm; all other measurements in mm. 'Distance ofanther from the tip ofthe perianth lobe.
White fir dwarf Red fir dwarf Wiens' dwarf
Character mistletoe mistletoe mistletoe
Female plants
Height 12.0 A 11.8 A 9.5 B
7.0 19.6 (200) 5.6-18.4 (100) 3.8-16.1 (130)
Basal diameter 3.7 A 3.6 A 3.2 B
2.3-6.4 (200) 2.4 6.1 (100) 1.8-5.8 (130)
Third internode 16.0 A 15.8 A 14.7 B
length 9.3 26.8 (200) 8.1-24.7 (100) 5.6-27.0 (130)
Third internode 2.2 A 2.1 A 1.9 B
width 1.5-3.1 (200) 1.4-3.0 (100) 1.3-2.9 (130)
Color yellow-green/yellow yellow-green/yellow/green- ;reen-brown/red-brown
brown
Male plants
Height 12.2 A 11.6 A 8.9 B
6.7-19.4 (200) 7.2-19.2 (120) 3.5 15.7 (160)
Basal diameter 3.6 A 3.5 A 3.1 B
2.2-6.1 (200) 1.9^.8 (120) 1.9-5.2 (160)
Third internode 15.9 A 15.4 A 13.5 B
length 7.0-23.8 (200) 9.9-24.4 (120) 5.4-23.0 (160)
Third internode 2.3 A 2.2 A 1.9 B
width 1.6-3.6 (200) 1.6-3.1 (120) 1.4-2.9 (160)
Color yellow-green/yellow yellow-green/yellow/green- green-brown/red-brown
brown
Staminate fiowers
—
Diameter 3-merous 2.6 A 2.7 A 2.4 B
— 2.3-3.0 (150) 2.4-3.1 (130) 2.0-2.9 (140)
Diameter 4-merous 3.5 A 3.5 A 3.2 B
3.1-4.0 (150) 2.6^.1 (130) 2.6-3.8 (140)
Perianth lobe length 1.3 A 1.3 A 1.2 A
1.1-1.7 (300) 1.0-1.9 (260) 0.8-2.0 (280)
Perianth lobe width 1.1 A 1.1 A 1.0 A
0.8-1.4 (300) 0.9-1.5(260) 0.7-1.4 (280)
Anther diameter 0.5 A 0.5 A 0.5 A
0.2 0.7 (300) 0.3-0.7 (260) 0.4-0.7 (280)
Anther distance' 0.4 A 0.4 A 0.6 B
0.2-0.6 (300) 0.3 0.7 (260) 0.4 1.0 (280)
Mature fruits
Length 4.7 A 4.6 A 4.2 B
3.3-5.6 (160) 3.7-5.7 (120) 3.1-5.0 (150)
Width 3.1 A 3.1 A 3.0 A
2.3-4.0 (160) 2.4-3.9 (120) 2.2-3.5 (150)
Color green, slightly glaucous green, slightly glaucous green to green-brown, slightly
glaucous
Mature seed
Length 2.5 A 2.5 A 2.4 A
1.9-3.3 (160) 2.0-3.3 (120) 1.9 2.9 (150)
Width 1.1 A 1.1 A 1.1 A
0.8-1.6 (160) 0.9-1.6 (120) 0.9 1.5 (150)
Color dark green dark green dark green
spruces were severely infected there. Many sites 6, 11, 14, and 16). It rarely infects western
severely infected Brewer spruces are present on white pine at Flat Top Mountain, but we have
the east slopes of Baldy Mountain as well as not found it parasitizing western white pine at
many dead spruces killed by the mistletoe. other locations where this tree is associated with
Wiens' dwarf inistletoe occasionally infects severely infected red fir or Brewer spruce. Our
white fir at Flat Top Mountain, Baldy Mountain, observations in the Sierra Nevada Mountains
Etna Suinmit, and South Fork Mountain (Fig. 1, fully support the earlier reports of the host
2009] MATHIASEN AND DAUGHERTY: ARCEUTHOBIUM ABIETINUM SUBSP. WIENSII 125
Table2. Principal MorphologicalandHostDifferences Between WhiteFir Dwarf Mistletoe, Red
Fir Dwarf Mistletoe, and Wiens' Dwarf Mistletoe. Mean plant heights in cm, all other means in mm.
'Host susceptibility system follows Hawksworth and Wiens (1972, 1996). Host classifications for Wiens' dwarf
mistletoe are based on data from field observations. Host classifications forwhite firdwarfmistletoe are based on
field observations and data presented in Hawksworth and Wiens (1996). Host classifications for red fir dwarf
mistletoe are based on data presented in Hawksworth and Wiens (1996).
Character White fir dwarfmistletoe Red fir dwarfmistletoe Wiens' dwarfmistletoe
Mean plant height
Male 12.2 11.6 8.9
Female 12.0 11.8 9.5
Mean basal diameter
Male 3.6 3.5 3.1
Female 3.7 3.6 3.2
Mean length ofthird internode
Male 15.9 15.4 13.5
Female 16.0 15.8 14.7
Mean fiower diameter
3-merous 2.6 2.7 2.4
4-merous 3.5 3.5 3.2
Mean fruit length 4.7 4.6 4.2
Anther distance from tip 0.4 0.4 0.6
Plant color:
Male yellow-green/yellow yellow-green/yellow/green-brown green-brown/red-brown
Female yellow-green/yellow yellow-green/yellow/green-brown green-brown/red-brown
Host susceptibility'
White fir principal host occasional host
Red fir immune principal host principal host
Brewer spruce immune unknown principal host
Western white pine rare host unknown rare host
specificity of the special forms of A. ahietiuiuu Although the distributions of A. ahietinwn
there. Because subsp. wiensii infects both red fir subsp. wiensii and f. sp. conco/oris overlap, we
and white fir, it is physiologically and genetically have not observed any areas where they are
distinct from both of the special forms. Further- sympatric. Incidence ofinfection ofwhite fir was
more, at three locations where f. sp. coucolovis consistently low (36^7%) in mixed red fir/white
was severely infecting white fir, it did not infect fir stands infested with subsp. wiensii. In contrast,
associated Brewer spruce (Fig. 1, sites 10, 12, and in stands with f. sp. conco/oris, incidence of
15). The absence ofinfection ofBrewer spruce by infection of white fir was common (>91%). In
f. sp. coucolovis is further support that it is addition, f. sp. conco/oris plants can easily be
genetically distinct from subsp. wiensii. distinguished from subsp. wiensii by plant size
The geographic range of subsp. wiensii does and color.
not overlap with f. sp. niagnificae and there is a Differences in plant size, geographic distribu-
distinct gap in the distribution of these dwarf tion, and host range have been the principal
mistletoes (Fig. 1). We have been unable to locate characters used to separate subspecies of Ar-
any infection ofred fir near Mt. Shasta or west of ceut/io/jiuni (Hawksworth and Wiens 1972, 1996;
there around Mt. Eddy, although red fir is Hawksworth et al. 1992; Wass and Mathiasen
common in these areas. Hawksworth and Wiens 2003; Mathiasen 2007, 2008; Mathiasen and
(1996) illustrated this geographic gap in their Daugherty 2007) and these are the principal
distribution map for red fir dwarf mistletoe (see characteristics that distinguish Arceut/iohium
their fig. 16.6). However, f. sp. conco/oris is ahietinwn subsp. wiensii from the special forms
common in these areas (Fig. 1, sites 18, 19, and ofA. a/iietinuni (Table 2). Because we also found
20 and see Hawksworth and Wiens 1996, fig. that the morphological siinilarities between the
16.3). Our map (Fig. 1) only includes the special forms of A. abietinum reported by
locations of populations we sampled during this Hawksworth and Wiens (1972, 1996) are consis-
study and is not meant to replace the distiTbution tent, particularly in the Sierra Nevada Mountains
map for f. sp. niagnificae in Hawksworth and wheie the special forms are often sympatric, we
Wiens (1996) which illustrates the location of concluded that describing these populations as
several other populations ofthis mistletoe. subspecies ofA. ahiefinmn was not appropriate.
MADRONO
126 [Vol. 56
Arceuthobium abietinum subsp. wiensii is and . 1996. Dwarf Mistletoes: Biology,
named in honor ofDelbert Wiens, ardent student pathology, and systematics. Agriculture Handbook
of Arceuthobium and one of the principal 709, USDA Forest Service, Washington, D. C.
contemporary architects of the genus. His col- , , AND D. p. Graham. 1967. Dwarfmis-
laboration with the late Frank Hawksworth tletoe on Brewer spruce in Oregon. Northwest
Science 41:42^4.
mspoasntneodfovtehre 2c5uryrrendtulryingrewchoigcnihzetdheyspdeecsicersibeodf wes,tern Nor,tAhNDAmeDr.icLa.nNtiaCxKaREoNfT.Arc1e9u92t.lwbNieuwm
Arceuthobium in Mexico and Central America, (Viscaceae). Novon 2:204-211.
as well as several taxa found in California that Mathiasen, R. L. 2007. A new combination for
many botanists and foresters recognize as distinct Hawksworth's dwarfmistletoe (Viscaceae). Novon
species (Hawksworth and Wiens 1993; Mathiasen 17:217-221.
and Marshall 1999, Hansen and Lewis 2000, . 2008. New combinations for Arceutliobium
aweum (Viscaceae) in Mexico and Central Amer-
Geils et al. 2002). ica. Novon 18:571-579.
Acknowledgments ANDC. M. Daugherty. 2005. Susceptibilityof
conifers to western hemlock dwarfmistletoe in the
We thank Dr. M. Socorro Gonzalez Elizondo for the Cascade Range of Washington and Oregon.
Spanish translation forthe Resumen andVictorLeshyk Western Journal ofApplied Forestry 20:94-100.
for help with the figures. AND . 2007. Arceutliobium tsugense
subsp. amabilae, a new subspecies of hemlock
Literature Cited dwarf mistletoe (Viscaceae) from Oregon. Novon
17:222-227.
Geils, B. W., J. Cibrian Tovar, and B. Moody. AND K. Marshall. 1999. Dwarfmistletoes in
2002. Mistletoes of North American conifers. the Siskiyou-Klamath Mountain Region. Natural
USDA Forest Service General Technical Report Areas Journal 19:379-385.
RMRS-GTR-98, Rocky Mountain Research Sta- NiCKRENT, D. L., M. A. GarIca, M. p. Martin, and
tion, Ft. Collins, CO. R. L. Mathiasen. 2004. Aphylogenyofall species
Hansen, E. and K. J. Lewis. 1997. Compendium of of Arceuthobium (Viscaceae) using nuclear and
conifer diseases. APS Press, St. Paul, MN. chloroplast DNA sequences. American Journal of
Hawksworth, F. G. and D. Wiens. 1972. Biology Botany 91:125-138.
and classification of dwarf mistletoes (Arceutho- Parmeter, J. R. AND R. F. SCHARPF. 1963. Dwarf-
bium). Agriculture Handbook 401, USDA Forest mistletoe on red fir and white fir in California.
Service, Washington, D. C. Journal ofForestry 61:371-374.
and . 1993. Viscaceae. Pp. 1092-1097 in Wass, E. F. and R. L. Mathiasen. 2003. A new
J. C. Hickman (ed.). The Jepson manual: higher subspecies of Arceutliobium tsugense (Viscaceae)
plants ofCalifornia. University ofCalifornia Press, from British Columbia and Washington. Novon
Berkeley, CA. 13:268-276.