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A taxonomic reevaluation of the genus Ostrya (Betulaceae) in the Southwestern
United States based on leaf morphology
Stephanie Dykema and Ross A. McCauley
Fort Lewis College, Department of Biology, Durango, CO
RESULTS DISCUSSION
LITERATURE CITED
ACKNOWLEDGEMENTS
Funding for this project was provided by the Fort Lewis College Faculty
Development Grant program. Research permits were granted by Grand Canyon
N.P., Guadalupe Mountains N.P., and Big Bend N.P. to R. McCauley.
BACKGROUND AND INTRODUCTION
METHODS
Ostrya is a genus of small deciduous trees in the birch family, Betulaceae, commonly
known as hop-hornbeam. The genus represents an ancient Holarctic plant distribution
and occurs in deciduous forests of Asia and Europe as well as in eastern North
America in abundance with isolated populations found in the dryer mountains of the
southwestern United States and NW Mexico, extending south as a cloud forest
endemic through central Mexico to Honduras (Furlow, 1990). The number of species
within North American Ostrya is small (3-5) and has been debated by systematists.
Ostrya populations in the eastern U.S. have been commonly recognized as Ostrya
virginiana (Mill.) K. Koch (Brain and Spamer, 2000) however, the grouping of
populations in the southwest has not been so easily agreed upon.
The isolated and disjunct occurrences of Ostrya across the SW US have led to the
recognition of one to three distinct species (Figure 1 & 2). Some botanists group the
southwestern populations under the single species Ostrya knowltonii Coville. The
genus has been further segregated, however, by some researchers based primarily on
geographic location and variation in fine-scale leaf morphology. Populations of the
Guadalupe Mountains have been referred to as O. baileyi Rose and populations
restricted to the Chisos Mountains in Texas and the Sierra del Carmen in Coahuila as
O. chisosensis. Under this segregated view O. knowltonii is restricted to the Colorado
River drainage in northern Arizona and southern Utah. No systematic study has been
conducted to consider the distinction of each population in relation to each other and
evaluate the validity of the proposed taxonomic delineation (Furlow, 1990).
Figure 2. Species of Ostrya illustrating habit, leaf morphology, and
reproductive structures. A. Collecting O. knowltonii near Moab, UT B.
Infructescence O. knowltonii, Alamo Canyon, NM C. O. baileyi with
staminate catkin at type locality in Dog Canyon, Guadalupe Mountains
National Park, TX D. O. knowltonii in Roaring Springs Canyon, Grand
Canyon National Park, AZ.
A.
Morphometric analyses of Ostrya in the SW US provides evidence that one variable
species likely exists in this region (Figure 3-6). Though several taxa have been
proposed for the SW US our data indicates that insignificant morphological variation
exists among populations across the region to support the segregation of species.
The distinction of O. baileyi in the Guadalupe Mountains and O. chisosensis in the
Chisos Mountains was based principally off of differences in the expression of stipitate
glands on the twigs and petioles with O. baileyi showing prominent glands and O.
chisosensis lacking these glands (Rose, 1905; Correl 1965). Additional variations in
leaf shape, leaf margin characteristics, and pubescence were also suggested (Furlow
1990) however, these characteristics were merely observed in few collected
specimens. Our field observations and morphological analysis indicated that these
characters are in fact variable within populations and thus do not serve as a means for
segregating taxon groups.
Phenotypic plasticity is likely responsible for much of the morphological variation
observed across the sampled populations. One particular example was the consistent
divergence of the Oak Creek Canyon, AZ population from the remaining O. knowltonii
populations. The ecosystem where this population grows is more moist and highly
vegetated than the open environments more commonly inhabited by Ostrya in the SW
(Figure 7). The larger trees and larger leaves are likely a physiological response to
lower light levels in this ecosystem which approaches the understory habitat of O.
virginiana and represents an inherent adaptability within the genome of the species.
This study supports the view that the SW US populations of Ostrya represent a single
taxon which should be referred to as Ostrya knowltonii Coville. Additional molecular
phylogenetic data for these populations inferred from four independent gene regions
additionally showed only minor nonspecific variation across the region (Bielz and
McCauley, 2013). Likely these isolated and disjunct occurrences represent relictual
habitat islands representing the remnants of a wider continuous distribution contracted
by long-term climatic changes.
Future investigations of morphological variation in North American Ostrya are needed
to test the hypothesis that isolated occurrences of Ostrya in the Madrean Sky Islands
and Copper Canyon region of NW Mexico represent a southern extension of O.
knowltonii. Additionally the circumscription and affinities of the cloud forest
occurrences across the Sierra Madre Occidental, Sierra Madre Oriental, and Southern
Cordillera of Mexico currently viewed as conspecific with O. virginiana need to be
evaluated. Figure 1. Distribution of Ostrya in
the SW United States and NW Mexico
based on herbarium records.
A B
A B
C
D
E
F
A.
Figure 6. Results of univariate morphometric analyses using 11 measured variables and 6 composite ratio
variables on leaf morphology in 10 populations of Ostrya. Shaded areas indicate the mean and 25th and
75th percentiles of the data with whiskers representing the 10th and 90th percentiles. Letters associated with
boxes indicate groupings of similar values determined through a Tukey Post Hoc Test (P<0.001). Several
characteristics show variation only between the Eastern populations and the Southwestern populations
however the WV and OH populations are significantly similar to most of the SW populations for the majority
of the measured characteristics. Variation between the Eastern O. virginiana and the Grand Canyon
populations as well as the Utah population can be seen for many of the characteristics. The Oak Creek
Canyon, AZ population is significantly different from the rest of the SW populations but similar to the
Eastern populations for petiole length and length of largest tooth and is significantly different from all other
populations for length of smallest tooth.
Figure 3. Multivariate analysis of ratio data. PCA. Centered data.
Log10 transformed. No pattern is apparent with the SW populations but
the O. virginiana of WV and OH show distinct segregation.
Figure 4. Multivariate analysis of continuous data. PCA. Centered data.
Log10 transformed. O. virginiana of the Eastern states shows clear
segregation. O. knowltonii of Oak Creek Canyon, AZ trends toward variation
of O. virginiana segregating from the remaining SW populations.
Figure 5. Multivariate analysis of continuous and discrete data. PCoA. O.
virginiana of OH and WV is distinctly segregated. The Oak Creek Canyon, AZ
population shows variation but is still united with the rest of the SW populations.
A B
C
D
BIELZ, A. and R. A. MCCAULEY. 2013. Using DNA barcoding to evaluate species circumscription in
the genus Ostrya (Betulaceae) in the southwestern US. Fort Lewis College Department of Biology
Senior Research Poster.
BRIAN, N.J. AND E.E. SPAMER. 2000. Knowlton Hop-Hornbeam Revisited (Ostrya
knowltonii Cov.). Bartonia 60: 49-56.
CORREL, D.S. 1965. Some additions and corrections to the flora of Texas. Wrightia 3: 126-129.
FURLOW, J. J. 1990. The genera of Betulaceae in the southeastern United States. Journal of the
Arnold Arboretum 71: 1-67.
ROSE, J. N. 1905. Notes on Ostrya, with two new species. Contributions from the United States
National Herbarium 8: 291-293.
• Ten populations representing all known areas of occurrence and each putative
taxon were sampled in the field during the summers of 2012 and 2013. Ten
branches, each from a separate tree, were collected from each population and were
pressed and dried for preservervation in the Fort Lewis College Herbarium (FLD).
• Morphological measurements were recorded for the largest leaf of each sample.
The following morphological characteristics were measured: petiole length (mm),
leaf lamina length (mm), leaf lamina width at widest point (mm), lamina width +30°
(mm), lamina width +60° (mm), lamina width -30° (mm), lamina width -60° (mm),
number of primary leaf veins (one side of leaf), stipitate glands on petiole (no=0,
yes=1), stipitate glands on leaf lamina (no=0, yes=1), abaxial pubescence desity
(lite=0, moderate=1, dense=2), adaxial pubescence density (lite=0, moderate=1,
dense=2), number of margin teeth (between the 3rd and 4th secondary veins on
one side of leaf), depth of largest measured tooth (mm), depth of smallest
measured tooth (mm). To eliminate gross size differences ratios were calculated
between total lamina length and width and lamina length and width at +30°, +60°, -
30°, and -60°.
• Univariate analyses were conducted by constructing box plots representing
variation within individual populations using SigmaPlot Ver. 12. Differences among
the means of populations were determined using a One-way Analysis of Variance
followed by a Tukey Post hoc test to determine significant differences using SPSS
Ver. 18.
• Three multivariate analyses were conducted using MVSP (MultiVariate Statistical
Package) Ver. 3.22: 1) Principal Components Analysis (PCA) of all continuous data.
Data was centered and log10 transformed. 2) PCA of ratio data. Data was centered
and log10 transformed and 3) Principal Coordinates Analysis (PCoA) including all
continuous and discrete data (minus ratios) using the Gower General Similarity
Coefficient.
Figure 7. Ostrya
habitat in Oak
Creek Canyon, AZ
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Le
af
Le
ng
th (
mm
)
20
40
60
80
100
120
140
160
A. Leaf Length a a
b b
c
b b
b b
b
c
c
c
c c c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Wid
th o
f L
ea
f (m
m)
10
20
30
40
50
60
70
80
B. Leaf Width a
a
b b
b b
b
b
b
c
c c c
c c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Wid
th o
f L
ea
f a
t +
30
° (m
m)
5
10
15
20
25
30
35
40
C. Width +30°
a
a
b b
b b
b
b
b
c
c
c
c c
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Wid
th o
f L
ea
f a
t +
60
°
0
10
20
30
40
50
60
D. Width +60° a a
b b b b
b
b
b
b
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Wid
th o
f L
ea
f a
t -3
0°
5
10
15
20
25
30
35
40
E. Width -30° a
a
b b
b
b b
b
b
b
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Wid
th o
f L
ea
f a
t -6
0°
(mm
)
0
10
20
30
40
50
F. Width -60° a
a b b
b
b b
b
b
b
c c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Pe
tio
le L
eng
th (
mm
)
0
2
4
6
8
10
12
14
G. Petiole Length a
b
a
a a a
a
b
c
c c
c
c c
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Nu
mb
er
of
Ve
ins o
n O
ne
Sid
e o
f L
ea
f
6
8
10
12
14
16
18
20
22
H. Number of Veins a a
b b
b
b b
b b
c
c c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
ynNum
be
r o
f T
ee
th B
etw
ee
n the
3rd
and
4th
Pri
ma
ry V
ein
s
2
4
6
8
10
12
14
16
I. Number of Teeth
a
a a
a a a
a
a a
b
b
b b
b
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Le
ng
th o
f S
ma
llest T
oo
th (
mm
)
0
1
2
3
4
5
J. Length of Smallest
Tooth
a a
a a
a
a a
a
b b b
b b
b b b
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Le
ng
th o
f L
arg
est T
oo
th (
mm
)
1
2
3
4
5
6
K. Length of Largest
Tooth a
a
a a
a
a a
b b
b
b
b b
b
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of L
ea
f L
eng
th to
Le
af W
idth
100
120
140
160
180
200
220
240
260
280
L. Length to Width
Ratio a
a a
b
a
b
a
c c
c c d d
d
d d d
d
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UMO D
og C
yn
O. b
aley
i - G
UMO P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of L
ea
f W
idth
at +
30
° a
nd
Le
af L
eng
th
20
22
24
26
28
30
32
34
36
38
40
42
M. Ratio of Leaf
Width +30°
a a
a a
a
b
b
c
c
c
c
c c
c
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UMO D
og C
yn
O. b
aley
i - G
UMO P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of L
ea
f W
idth
at -3
0°
and
Le
af L
eng
th
20
25
30
35
40
45
N. Ratio of Leaf
Width -30°
a a a
a
a
a a
b
b
b b
b b
b
c
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UMO D
og C
yn
O. b
aley
i - G
UMO P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of L
ea
f W
idth
at +
60
° a
nd
Le
af L
eng
th
25
30
35
40
45
50
O. Ratio of Leaf
Width +60°
a a
a
a a
b
b c
c
c
c
c
c c c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UMO D
og C
yn
O. b
aley
i - G
UMO P
ine
Springs
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of L
ea
f W
idth
at -6
0°
and
Le
af L
eng
th
20
25
30
35
40
45
50
55
60
P. Ratio of Leaf
Width -60°
a a a
a a
b
b c c
c c c c
c
O. v
irginiana
- W
V
O. v
irginiana
- OH
O. b
aley
i - G
UM
O D
og C
yn
O. b
aley
i - G
UM
O P
ine
Spr
ings
Cyn
O. c
hiso
sens
is
O. k
nolw
tonii -
Alam
o Cyn
O. k
nowlto
nii -
UT
O. k
nowlto
nii -
GRCA B
right
Ang
el
O. k
nowlto
nii -
GRCA R
oarin
g Spr
ings
O. k
nowlto
nii -
Oak
Cre
ek C
yn
Ra
tio
of N
um
be
r o
f T
ee
th B
etw
ee
n 3
rd a
nd
4th
Pri
ma
ry V
ein
s a
nd
Le
af L
eng
th
0
5
10
15
20
25
30
Q. Number of Teeth
Ratio
a a
a a
a
a
a
a
b
b
b
b
b b
b b
The purpose of this study was to
examine the distribution and
morphological variation of Ostrya in the
southwestern United States to gain a
clear understanding of the taxonomic
delineation of the species. This work
represents a contribution to an ongoing
systematic revision of the genus across
North America and consisted of
morphometric analyses of leaf form
across ten populations of Ostrya.