Morphological and Isoenzyme Variation in Rhododendron occidentale (Western Azalea) (Section Pentanthera; Ericaceae)

2012·11.4 MB·English

by  G F Hrusa

Madrono, Vol. 59, No. 3, pp. 128-142, 2012
MORPHOLOGICAL AND ISOENZYME VARIATION IN RHODODENDRON
OCCIDENTALE (WESTERN AZALEA) (SECTION PENTANTHERA; ERICACEAE)
G. F. Hrusa
UC
Davis Center for Plant Diversity, Department of Plant Sciences, Mail Stop 7, One
CA
Shields Avenue, Davis, 95616
California Dept. of Food and Agriculture Plant Pest Diagnostics Center, 3294 Meadowview
CA
Rd., Sacramento, 95832-1448
[email protected] gov
.
Abstract
Morphological and isoenzyme variation among populations of western azalea. Rhododendron
&
occidentale (Torr. A. Gray) A. Gray, were examined. Three regional parapatric groups were revealed:
1) the northern California outer North Coast Ranges; 2) the northern California and southern Oregon
Klamath Ranges; and 3) the central CaUfornia Sierra Nevada and southern California Peninsular
A
Ranges. highly variable but generally intermediate fourth group is restricted to ultrabasic substrates
(serpentine) in the middle and inner North Coast Ranges ofCalifornia. It is comprised ofpopulations
with recombined morphologies and alleles that were otherwise restricted to one or more of the three
A
groups above. revised intraspecific treatment is proposed, with the three regional groups above
&
recognized as varieties. These are: R. occidentale (Torr. A. Gray) A. Gray var. occidentale (outer
North Coast Ranges), R. o. var. paludosum Jeps. (Klamath Ranges), and Rhododendron, occidentale
&
var. californicum (Torr. A. Gray) Hrusa comb, et stat. nov. (Sierra Nevada and Peninsular Ranges).
Lectotypifications of Azalea occidentalis Torr. & A. Gray isotypes at PH and GH, Azalea californica
Torr. & A. Gray in Durand, and Rhododendron sonomense Greene (NDG) are also provided.
Key Words: Azalea, isozyme, lectotype, morphometric, population, Rhododendron occidentale.
In addition to its large and fragrant flowers 1977), which are sold with names such as
&
Rhododendron occidentale (Torr. A. Gray) A. 'Humboldt Picotee', 'Tatum's Pink', or 'Double
Gray has long been recognized for its diversity of Dig Twelve' (Jones et al. 2007). Accompanying
growth habits, floral pigmentations, and vegeta- the reports of these variants' discoveries were
tive forms (Kellogg 1855; Wilson and Rehder poorly documented assertions regarding poly-
1921; Jepson 1939, Munz and Keck 1959; Moss- ploidy; wild distributions; regional variation
man and Smith 1969; Kron 1993). The only more patterns; and edaphic, moisture, and temperature
or less invariant characteristic is the presence of a tolerances in wild populations (Breakey 1960;
yellow nectar guide on the upper corolla limb. It Mossman and Smith 1968; Mossman 1972, 1974,
has been suggested that this variation indicates 1977). Ultimately, experimental evidence for any
the existence of multiple species (Mossman and of these interpretations is lacking.
Smith 1969; Mossman 1977). Other observers
have interpreted these polymorphisms as ran- Geographic Distribution
domly distributed genotypes or as environmen-
tally induced (Breakey 1960). The most recent Rhododendron occidenta/e is distributed within
systematic treatment of section Pentanthera the Coast Ranges of Cahfornia, the Klamath
(Kron 1993) did not examine the presence or Ranges of northern California and southern
patterns of intraspecific variation in R. occiden- Oregon, the Sierra Nevada, and the Peninsular
tale, and the same can be said of the discussion in Ranges of southern Cahfornia. Its distribution is
Wilson and Rehder (1921). Indeed, there has largely coincident to the California Floristic
&
been no detailed accounting of its regional Province (CFP) (Raven Axelrod 1978) with
diversity. its northernmost populations only about 75 miles
In horticultural circles its visible morphological north of the CFP along the Umpqua River in
variation has made R. occidentale a favorite of Douglas Co., Oregon. It is found at elevations
azalea breeders. Middle nineteenth- to early extending from sea level to near 2800 m.
twentieth-century selections were prominent in Throughout its range it is restricted to sites of
these breeding programs (Mossman 1974). The permanent moisture, although these may be
results can be found for sale as the Knapp Hill subsurface sources. It is frequently found growing
and Exbury hybrid series. More recently, enthu- on ultrabasic soils, predominantly serpentine,
siasts have been seeking out novel wild forms. particularly in the Klamath ranges and inner
Especially popular are those with unusual corolla North Coast Ranges. Except for a single location
shapes and color variations (Mossman 1974, at the northern tip of the Gabilan Range in
.
2012] HRUSA: VARIATION IN RHODODENDRON OCCIDENTALE 129
Monterey Co., R. occidentale is absent from the types and their positions, in addition to quanti-
California South Coast Ranges and Transverse tative physical data (Sleumer 1949; Kron 1993).
Ranges. It is presumed that the warming and The first two proved particularly useful in this
drying of the post-Pleistocene eliminated it from study.
these relatively dry mountains. Claims that R. Quantitative data were taken from specimens
occidentale has native populations in the Puget collected, pressed, and dried specifically for these
Sound area, the Olympic Peninsula, and on analyses. Because of the variable bilateral form of
Mount Rainier in Washington (Mossman 1974) Rhododendron occidentcde corollas, special han-
require confirmation. dling and pressing ofindividual flowers after their
This paper will present quantitative and removal from the inflorescence was necessary for
qualitative analyses that describe the patterns of consistent measurement of corolla tube and limb
morphological and isoenzyme variation among relationships. For the quantitative characters, val-
A
wild populations of R. occidentale. taxonomic ues were defined as the mean of four measure-
treatment that accounts for the species' natural ment repetitions per structure per individual. As
variation patterns will also be proposed. much as possible each measured structure was
standardized by plant position and developmen-
Materials and Methods tal stage. Phenotypic plasticity within leaf size,
shape, venation patterns, and trichome length
Sampling were demonstrated in a preliminary unpublished
study (Hrusa 1991). Seed and capsule features
Populations representing the species' full geo- including seed wing shape and capsule sizes and
graphic range were analyzed. Thirty-six popula- shapes were highly variable within individuals and
tions were used for the morphological analysis, were not used.
and 37 populations were used for the isoenzyme The raw measurements were taken at various
analysis (Fig. 1 and Appendix 1). scales. These were ranged to between 0 and 1
All but three population samples contained a using Gower's Transformation (Sneath and
minimum of 25 individuals. The three smaller Sokal 1973). The population-based quantitative
samples came from critically situated populations characters were defined as the proportion of the
that did not contain that many individuals. range for a given population that fell in two of
Rhododendron occidentcde is not rhizomatous, three equal classes that represented the upper and
nor does it sprout from the roots. It may, however, lower one-third of the structure's among-popu-
form clones when fallen trees or branches press
lation range. Statistically, the central of the three
plants to the ground and adventitious roots develop.
quantitative classes for each character is always
There was adequate visible variation among indi- correlated to one of the outside thirds, and was
viduals in both growing and dormant structures so
excluded.
that duplicate clone collections were readily avoid-
The qualitative character states were defined as
ed. Sampling was random throughout except in the
their frequency within each population sample.
case of the smaller populations where every
Corolla coloration data were acquired from fresh
individual was examined.
material. Trichome position and density data
The morphological samples included both
were taken from dried specimens. The quantita-
spring-collected flowering material and winter-
tive and qualitative characters are listed in
collected dormant inflorescence buds. Thus the
Table
dormant and flowering collections used for mor- 1.
phological examination did not necessarily repre-
sent the same individuals. This did not affect the Isoenzyme Data
analyses because the characters were defined as
population summaries. Specimens for isoenzyme Soluble enzymes were extracted from fresh
analysis were either fresh, spring-collected corolla plant samples and electrophoresed on horizontal
tissue or mature, dormant vegetative branch tips. starch gels composed of 12% hydrolyzed potato
The sampled populations are mapped in Figure 1 starch and 3% sucrose. GeMl and electrode buffeMrs
Locality descriptions and sample sizes are listed in were composed of0.0009 L-histidine-0.0003
M M
Appendix 1, and representative vouchers from citric acid and 0.065 L-histidine-0.019 citric
those populations have been deposited at CDA acid, both at pH 5.7. Electrophoresis proceeded
and DAV. All statistical analyses were performed for 13 hours at 3.5 watts.
in JMP 5.1 (SAS Institute). Allelic variants were classified and identified by
their relative migration distance against a stan-
Morphometric Data dard allele at each locus. This allele was one
present in every population and was usually the
Traditional morphological classifications of most common. Homologies among the variant
Rhododendron have emphasized variation in electromorphs were determined by comparing
floral pigmentations and vegetative trichome them on common gels.
MADRONO
130 [Vol. 59
Fig. 1. Populations of Rhododendron occidentale used in the morphological and isoenzyme analyses. See
Appendix 1 for geographic location and sampling details.
Results both each other and from the SNPR populations.
With two exceptions, the inner North Coast
Morphological Variation Range Serpentine (INCRS) populations plotted
between the ONCR, KR, and SNPR popula-
Thirty-eight outwardly visible features (21 tions, much as they are situated geographically
quantitative and 17 qualitative) were described (Fig. 3). The exceptions, (P-64, Kilpepper Creek,
and measured or assessed (Table The among- Lake Co.; and P-34, Stony Creek, Colusa Co.)
population comparisons were perf1o).rmed through grouped among the SNPR populations. These
SNPR
principal components analysis of the among- two populations shared with those of the
population correlation matrices. the characteristics of relatively long, generally
The first three principal components describ- white-colored corolla tubes, and a pubescent leaf
ed 84.9% of the total variation, with four clus- abaxium.
ters of populations evident. These are plotted in Stepwise discriminant analysis was used to
Figure 2 and mapped in Figure 3. The Sierra evaluate which characters were useful in distin-
Nevada and Peninsular Range populations guishing the four groups in Figure 2. The results
KR
(SNPR) grouped together. The populations of indicated that individuals from the and
ONCR
the Klamath Ranges (KR) and outer North populations shared combined glandular
Coast Ranges (ONCR) ordinated apart from and eglandular multicellular trichomes on the leaf
2012] HRUSA: VARIATION IN RHODODENDRON OCCIDENTALE 131
TABLE 1. Definitions of Morphological Features Used in the Multivariate Analyses. Asterisks (*)
denote subset ofnine systematically useful characters. Quantitative characters were defined as described in the text.
Qualitative characters were defined as their frequency within the population sample.
Quantitative Qualitative
1. Ovary length: classes 1, 3 11. Perianth tube: dark pink *20. Leaf abaxium, secondary vein
trichomes: absent
2. Anther length: classes 1, 3 12. Perianth veins: pink base to 21. Leaf margin trichomes: mixed
summit glandular and strigose
3. Corolla length: classes 1, 3 13. Perianth veins: white except *22. Floral bud-scales, margin
for vein tip trichomes: glomerate
4. Corolla tube length: 14. Perianth limb: pink *23. Floral bud-scales, margin
classes 1, 3 trichomes: ciliate
5. Corolla length/tube length 15. Perianth limb: white *24. Young twigs, vestiture: densely
ratio: classes 1, 3 pubescent
6. Inflorescence bud length: *16. Leaf abaxium, midvein *25. Young twigs, vestiture: glabrous
classes 1,3 trichomes: mixed glandular
and strigose
7. Calyx lobe length, longest: 17. Leaf abaxium, midvein *26. Leaf abaxium, surface: single-
class 1 trichomes: glandular celled pubescence
8. Calyx lobe length, shortest: 18. Leaf abaxium, secondary 27. Floral bud bract, surface vestiture:
class 1 vein trichomes: mixed glandular pubescent
and strigose
9. Calyx lobes ratio, length of *19. Leaf abaxium, secondary vein 28. Floral bud bract, surface vestiture:
longest/shortest: class trichomes: strigose glabrous
1
*10. Leaf abaxium, multicellular
trichomes per 25 mm^: class 1
(<7) and 3 (>26)
abaxial midvein and a lamina abaxium without pubescence on the leaf abaxium (KR azaleas are
unicellular hairs. There may occasionally be generally glabrous abaxially) and 2) midvein
unicellular trichomes on and adjacent the mid- trichomes of a single type only (these are usually
ONCR
vein, but not on the abaxial surface. The mixed strigose and glandular in the KR). The
populations alone were distinguished by: 1) a presence of these two morphological states
dense pubescence on the young twigs and suggests plants of the SNPR populations. How-
dormant bud bracts; 2) winter bud bract-margin ever, isoenzyme alleles characteristic of that
trichomes always of a glomerate-glandular type; group were absent.
3) relatively large dormant flower buds; and 4) The SNPR azaleas had: 1) one type of
more than 25 multicellular trichomes per/25mm- multicellular leaf midvein trichome, either glan-
of leaf abaxial surface. The distinguishing fea- dular or eglandular, not those combined as in the
tures are marked with an asterisk in Table 1 and KR and ONCR; 2) a unicellular pubescence
with additional morphological features summa- throughout the lamina abaxial surface; 3) second-
rized among the groups in Table 3. ary vein multicellular trichomes of the same type
Klamath Ranges populations alone were dis- as the midvein (glandular or eglandular); 4)
tinguished by: 1) mostly glabrous young twigs absent or widely scattered multicellular trichomes
«
and either glabrous or thinly ciliate bud bracts; 2) on the tertiary veins (when present these were
usually ciliate, occasionally glomerate winter bud 25/25 mm^); 5) a non-pigmented to rarely, slightly
bract-margins; 3) generally a pink- to red- pigmented corolla tube; 6) corolla veins rarely
pigmented corolla tube; 4) a short corolla tube with more than a hint of pigmentation at the
SNPR
length in relation to the throat plus limb; and 5) distal tip. In general, corollas were either
the lamina abaxial surface, excluding the mid- pure white or (infrequently) had a hint of pink in
vein, was devoid or nearly so of trichomes. the tube or vein summit; and 7) the corolla tube
Populations from the immediate coast generally was comparatively long in relation to the com-
were transitional to the ONCR azaleas (glome- bined limb and throat. The SNPR plants were
rate bud bract-margin trichomes and less densely thus particularly distinctive morphologically.
KR
pubescent bud bracts and twigs). Overall the Only P-50 (Butterfly Valley, Plumas Co.) of the
azaleas had the smallest corollas with the shortest northern Sierra Nevada had glabrous leaf abaxia
floral tubes and the most pink to red pigmenta- and often glabrous young twigs, both features
tions in the limb and tube. Among the KR unusual among the Sierran azaleas. Population 50
populations, only the single northernmost and plotted between the SNPR and KR populations,
most interior was morphologically unusual (P-25, the same as it is situated geographically (Fig. 3).
Cow
Creek, Douglas Co. Oregon, Fig. 2). This In general, the southern Cahfornia Peninsular
population had: 1) infrequently, a unicellular Range azaleas had the largest and least pigmented
MADRONO
132 [Vol. 59
5-
INCRS
4-
SNPR
* • ONCR
O KR
^36
• O O
r,_
° 9 43 o
-
-1
Fig. 2. Scatter plot of the first three principal component scores for the morphological dataset. Populations 64
and 34 occur in the inner North Coast Ranges on serpentine, plotted here with Sierra Nevada populations. Labeled
populations are discussed in the text.
flowers with the longest floral tubes. Overall, seedlings, indicating it is under genetic control,
excluding the INCRS azaleas, a dine exists from at least in the INCRS (Hrusa 1991). Although
north to south in which corolla coloration the non-INCRS anthocyanin pigments were not
diminishes and the corollas become larger overall as dark as that among individuals within the
and have relatively longer tubes. INCRS populations, this distinction could not be
Even excluding P-34 (Stony Creek, Colusa Co.) consistently delimited into a set of qualitative
and P-64 (Kilpepper Creek, Lake Co.) that categories. Such coloration is a feature of many
ordinated among the SNPR, the INCRS popu- ultrabasic-adapted taxa (Kruckeberg 1984).
lations were weakly differentiated. They were Strongly bifacial leaves that were lighter on
distinguishable morphologically only by a short- the abaxial surface characterized many popu-
mm
est calyx lobe that was generally less than 1 lations, mostly those of the SNPR. Several
in length, and sometimes nearly obsolete. Their INCRS populations were similarly bifacial.
multivariate scattering across the space between Some of the latter were dimorphic for that char-
the KR, ONCR, and SNPR groups (Fig. 2) was acteristic, and in those populations the intensi-
the result of both quantitative intermediacy and ty of the bifacial condition was particularly
mosaic patterns among the qualitative features. variable, often varying in intensity even within
This variation was spread among the first three individuals.
principal components and is suggestive of segre- The timing of flower bud opening relative to
gation and recombination among the analyzed leaf break is generally species specific within
features. Rhododendron section Pentanthera (Kron 1993).
Definitions of three readily visible and at least Inflorescences may open concurrently to or after
partially regionally distinctive features proved foliage maturation. In R. occidentale both condi-
KR
problematic and were not included as population- tions occur. Plants of the and most of the
level characters in the multivariate analyses. INCRS open flowers and leaf buds concurrently.
Darkly anthocyanous new growth was a distinc- Exceptions may occur in densely shaded plants
tive feature ofboth sun- and shade-grown INCRS where bud (and often leaO break may be delayed.
azaleas. Elsewhere, azaleas growing on ultrabasic- However, most followed the pattern of inflores-
derived soils often had at least some anthocyanin cence break in concert with foliar emergence. One
pigmentation in the young twigs, particularly in population from the INCRS (P-64, Kilpepper
plants growing in full sun. This pigmentation Creek, Lake Co.) broke flower buds only after
(and lack of same from non-pigmented popula- new growth had fully matured; yet plants in the
tions) was maintained in greenhouse-grown closely related and nearby P-34 (Little Stony
2012] HRUSA: VARIATION IN RHODODENDRON OCCIDENTALE 133
Fig. 3. Map of the population clusters based on morphological variation as identified in Fig. 2. Labeled
populations are discussed in the text.
Creek, Colusa Co.) opened concurrent to bud Isoenzyme Variation
break. With one exception each, plants of the
ONCR and SNPR opened their inflorescences Forty-two alleles were resolved at seven loci
after the fohage had fully expanded and matured. from four enzyme systems. The resolved variants
Only the ONCR P-45 (Hogback Mountain, were in malate dehydrogenase (MDH-1, MDH-2,
Sonoma Co.), growing on a highly insolated MDH-3, total alleles), phosphoglucomutase
1 1
and relatively dry hillside, pushed its flower buds (PGM-1, PGM-2, 6 total alleles), 6-phosphoglu-
late-concurrent to leaf break. Again with one conate dehydrogenase (6-PDH, locus, 5 total
1
exception. Sierra Nevada populations flowered alleles), and glucose-6-phosphate-isomerase
after leaf maturity. Population 49 (Pulga Rd., (GPI-2, 20 total alleles).
Butte Co.), from an open, south-facing serpentine At each locus there was a most-frequent
slope, opened its flowers with new growth (primary) allele with the remaining allele(s) at
expansion. Thus, while bud and leaf break lower frequencies. The presence or absence and
patterns are mostly consistent regionally, the frequency of the alternate alleles varied widely
exceptions suggest that local environmental among populations. Only in P-64 (Kilpepper
conditions or selection in open habitats influence Creek, Lake Co.) and P-61 (Cuyamaca Peak, San
PGM
timing of flower bud break. Diego Co.) did the alternate alleles at
MADRONO
134 [Vol. 59
INCRS
64 ASNPR
6-,
•ONCR
OKR
34
36
2-
0-
s
'
o*43
O o
-2- •o
O
52
o
12 -10 -8 0
Fig. 4. Scatter plot ofthe first two principal component scores for the isoenzyme dataset. Labeled populations are
discussed in the text.
exceed slightly the frequency of the primary frequencies than all but one population outside
allele. In no case did an alternate allele replace that group.
the primary one. Two populations of the North Coast Ranges
The first three principal components recovered also classified differently between the morpho-
95.0% of the variation. Three population groups logical and isoenzyme datasets. Population 43
were evident, as opposed to four for the (Wildwood, Trinity Co.), the northernmost mor-
morphological data. The groups are plotted in phologically like the INCRS group (Figs. 2, 3),
Figure 4 and mapped in Figure 5. contained allelic complements characteristic of
The multivariate patterns were similar to those the KR, not those of the INCRS.
using morphology, except for the superposition Population 52 (Red Mountain, southern Hum-
KR ONCR
of the and populations. With five boldt Co.) grouped morphologically among the
KR KR
endemic alleles the group might have been populations. However, its isoenzyme com-
expected to occupy its own isoenzyme multivar- plement placed it between the SNPR and KR +
ONCR
iate space as it did its own morphological space. populations, but on the opposite side of
That it does not is due to the presence ofthe non- the multivariate space occupied by the likewise
private endemic alleles in only a few populations, intermediate INCRS group (Fig. 4). Although P-
and at relatively low frequencies. 52 contains the same SNPR and KR alleles that
The SNPR and INCRS populations plotted characterized most of the populations included
over a broader multivariate space than did the here in the INCRS, it was distinguished from
KR ONCR MDH-2E
adjacent + cluster, due to their them by a high frequency of allele and
greater allelic diversity and higher alternate allele a low frequency of MDH-3B, the reverse of the
frequencies. Moreover, those frequencies varied frequencies found in the INCRS populations.
considerably among the populations. In terms of Overall P-52 has mostly KR alleles. Its SNPR
allele presence or absence the SNPR and INCRS connection is via relatively high frequencies of
were similar. However, the shared alleles were not alleles PGM-2B and PGM-2A as found through-
at similar frequencies, and this is responsible for out the SNPR and INCRS populations.
their plotting in a slightly different, but adjacent, In relation to the four geographic regions
multivariate space. A characteristic INCRS allele evident in the morphological analyses, four allele
was MDH-3B; although this allele was also found distribution patterns were discernible: 1) wide-
widely scattered at generally low frequencies spread, not ubiquitous, but occurring across
among the KR, SNPR, and ONCR populations, geographic regions; 2) alleles common in one
it was in every INCRS population and at higher region, but uncommon and localized in another,
2012] HRUSA: VARIATION IN RHODODENDRON OCCIDENTALE 135
Fig. 5. Map of population clusters based on isoenzyme allele variation as identified in Fig. 4. Labeled
populations are discussed or mentioned in the text.
sometimes disjunct region; 3) endemics, restricted at PGM-2 in the SNPR + INCRS versus those of
to multiple populations within a single region, the KR + ONCR, the distinction of these two
but absent elsewhere; and 4) private alleles combination groups is supported by allele pat-
known only from a single population. terns at other loci, and by morphology.
Systematically, PGM-2 was the most distinc- Among the 42 total alleles identified, seven
tive. The SNPR and INCRS populations had were restricted to the KR region, of which two
three PGM-2 alleles (PGM-2A, PGM-2B, and were private and five were shared among at least
PGM-2C) all at more or less equal frequencies. In two populations (endemic alleles). Nine total
ONCR KR SNPR
contrast, the and populations con- alleles were restricted to the region; four
tained exclusively or were dominated by PGM- endemics and five private. While there were also
2C, the most frequent allele at PGM-2. This three private alleles (all P-61, Cuyamaca State
PGM-2 dichotomy between the KR + ONCR Park, San Diego Co.) and one endemic allele not
and SNPR + INCRS was consistent throughout found in the Sierra Nevada that occurred among
the species' range. The pattern was maintained the Peninsular Ranges populations, there were
even when the populations were in geographic also several alleles shared between those two
proximity, a situation suggestive of restricted regions that did not extend beyond them.
gene flow. Whatever is ultimately responsible for Two private alleles were in population 36
the consistently different allele frequency patterns (Gilliam Creek, Sonoma Co.) of the INCRS,
MADRONO
136 [Vol. 59
TABLE 2. Variant Alleles Occurring in the Incrs Populations and their Distribution Outside that
Group. 'X' = alleles found in at least one population within the group at a frequency above 0.100 (10%); =
alleles not found in that group at a frequency above 10%.
Geographic regions
INCRS SNPR KR ONCR
Allele
X
PGI-2^ +
X X
PGI-2^
X X
PGI-2'
X X X
PGI-2^
X X
PGI-2^
X X
PGI-2"^ +
X X X
PGM-2^ +
X X
PGM-2'^ +
MDH-P X +
MDH-1^ + X
X
MDH-2'^ + +
X X
MDH-3'^ + +
X X
6-PDH''
X
6-PDH'^ + +
Total shared + (%) 14 11 (78.6) 8 (57.1) 4 (28.6)
Shared at >10% + (%) 12 7 (63.6) 2 (25.0) 4 (100)
Shared, both >10% (%) 6 (50) 1 (8.4) 4 (33.4)
KR ONCR
but no endemic alleles occurred among the Second, while the and azaleas had
INCRS populations. Likewise, neither private similarly low frequencies of alternate alleles, the
nor endemic alleles occurred within the ONCR. allele complements were different. Morphologi-
cally, the azaleas of these two regions were quite
Discussion distinct. It may be instructive here that Kron et.
al. (1993) found no allelic differences (or variants)
PGM
From the data, four main points may be made. at enzyme systems GPI and between
First, it is clear that the azaleas of the Peninsular Rhododendron canescens (Michx.) Sweet and R.
Ranges are allied to those of the Sierra Nevada. flammeuni (Michx.) Sarg., two morphologically
This is not surprising given the floristic, geologic, quite distinct species. In R. occidentale, some
and climatic similarities of the forested parts morphological intermediacy occurred along the
of the two regions (Munz 1974; Axelrod 1976; immediate coastline north of Fort Bragg, Men-
Raven and Axelrod 1978). Azalea populations of docino Co. There the pubescent new growth and
the Sierra Nevada and Peninsular Ranges shared outer dormant flower bud bracts of the adjacent,
a distinctive allele frequency pattern at PGM more southern ONCR azalea appeared as a thin
where the two region's populations all had pubescence in populations that otherwise were
KR
relatively equal frequencies of three different Uke the more frequently glabrous azalea.
alleles. In contrast only one of the two alternates These northern coastal azaleas did not have the
was even a rare occurrence in either the KR multicellular leaf tertiary vein trichomes that
or ONCR populations. Despite the presence of were generally characteristic of the ONCR, and
endemic GPI alleles in some Peninsular Range their isoenzyme complements were those of the
azaleas that suggests a long post-disjunction KR. As is true for the Sierra Nevada azaleas, the
ONCR KR
history, their morphological similarity to the and populations are each associated
azaleas of the Sierra Nevada, particularly the with certain distinctive forest taxa such as
high southern Sierra Nevada, was marked. It Sequoia sempervirens (D. Don) Endl.and Cupres-
would appear that these two regions were sus (Chamaecyparis) lawsoniana A. Murray bis,
formerly part of a continuous interbreeding respectively. Based on the fossil record (Axelrod
azalea population. Fossil azaleas of Pliocene age 1962, 1976; Raven and Axelrod 1978), these taxa
(pre-Sierra Nevada time) were found in the Chalk and their associates occupied widespread geo-
Hills flora of western Nevada (Axelrod 1962). graphic regions long before being restricted to
These azaleas were associated with Sequoiaden- their current distribution in west coast cismon-
dron and other montane taxa that the western tane habitats.
azalea is associated with in the Sierra today. Third, shared endemic alleles, similar within-
However, Coast Range elements, including the population allele frequencies (as at PGM-2), and
Monterey Co. endemic Abies bracteata were also certain distinctive morphological features such as
present. The leaf and capsule impressions were the superimposition of glandular and non-glan-
KR ONCR
examined by this author, but are not assignable dular trichomes in + in contrast to
below section Pentanthera. restriction of those trichome types to different
I >
2012] HRUSA: VARIATION IN RHODODENDRON OCCIDENTALE 137
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