Table Of ContentRHODORA,
Vol No. 268-290, 1991
93, 875, pp,
AND REPRODUCTION
SEXUAL
VEGETATIVE IN
POLYMORPHA
THE RARE CAREX
SEDGE,
(CYPERACEAE)
and Dudley
Standley Judith
Lisa A. L.
ABSTRACT
Carcx polymorpha a rare sedge of eastern North America, currently a can-
is
Maine and Massachusetts were studied
Populations
didate Tor Federal listing. in
population monitoring, management, and pro-
establish a scientific basis for
to
We
examined potential and actual fecundity, and used pollination ex-
tection.
periments hypotheses regarding breeding systems. Sexual reproductive
to test
common
compared Studies of vege-
characters were with the species, C. vcslita.
C
reproduction of polymorpha included determination of rhizome growth
tative
above- and below-ground biomass, organ dimensions and dynamics of
patterns,
permanent
shoots in plots.
Both vegetative growth and sexual reproduction appear to be correlated with
canopy Numbers of flowering shoots, flowers and seeds appear to be
closure.
Hmited by light availability. Both the number of achenes and the percent seed set
C
Carex polymorpha and Density of
per flowering shoot are similar in vestila.
canopy
vegetative shoots and of leaf and rhizome sizes are also correlated with
Shoot dynamics
over: biomass production appears to be limited by light levels.
c
are correlated with light and microhabitat type. The least stable shoot populations
open
are disturbed, open sand sites, while shoot populations in undisturbed,
in
canopy have high turnover rates but stable sizes. These results suggest that
sites
may and
canopy management be maintenance of vegetative sexual
critical to
Carex polymorpha.
reproduction established populations o{
in
Key Words: Carcx, rare species, reproductive biology, vegetative reproduction,
Maine, Massachusetts
INTRODUCTION
Don)
Carex polymorpha Muhl. Paniceae G. a rare
(section
is
from
sedge with fewer than 30 extant populations distributed
Maine West Virginia, Hsted as rare in each of the states
to
It is
known have Carex
which occur or occurred. poly-
to to
in
is
it
and WildHfe
morpha has been under review by the U.S. Fish
when was
Service for Federal listing since 1983 placed in cat-
it
may
which be appro-
egory comprised of those taxa for listing
2,
but which substantial data on biological vulnerability
priate, for
The
primary
and needed goals
threats arc to ascertain their status.
on and popu-
of study were provide data the histoid
this to life
lation dynamics of this rare sedge that would be of value in efforts
268
Dudley— 269
and
Standley C<3rex
1991]
monitor populations and develop recommendations for
to
to
management and
protection
strategies.
Don
Carex
Paniceae G. group of approximately 12
Section a
is
North America
and North America.
of Eurasia In this
species
European adventive Carex panicea and
section includes the L.
several widely distributed species of neutral or calcareous habitats
(C
(Wahl.)
that are, however, listed as rare in several states livida
WA, NY; NY;
Willd., C. meadii Dewey, C. tetanica Schkuhr.,
C
NY; Dewey, Other
lA; C. vaginata Boott, woodii lA). species
bdtmoreana Mackenz.,
included in section Paniceae are C. a rare
southern Appalachian endemic of wet shaded in the Blue
cliffs
Mountains
from
Florida to North Carolina; and C. californica L. H. Bailey, a rare
Carex
occurring from northwestern California to Idaho.
species
C
polymorpha.
californica appears to be the closest relative of It
and most
morphologically very similar vegetative floral
in all
is
and and non-oblique beak
characters, differs only in the shorter
of the perigynium.
Carex polymorpha
Preliminary observations of populations of
New
Rhode and
Hampshire,
Maine, Massachusetts, Island,
in
Pennsylvania led us to develop the hypothesis that variation in
canopy
seed and vegetative growth correlated with
flowering, set is
and
To hypotheses, observations of plants
cover. test these field
two Maine
experimental manipulations were performed at sites in
Permanent were
and one Massachusetts. plots established to
in
study shoot history, density and turnover of shoots. Destruc-
life
on
sampling of additional plots provided data vegetative
tive
rpholo
We
com
flowering shoots.
recruitment
limited
most important maintenance of existing populations.
factor in
we
To Carex polymorpha,
characterize reproductive biology in
,amy
systems
among and
environmental
life-history
vestigated correlations
He
characteristics and fruit set in plants. found that fruit set is
270 Rhodora
[VoL 93
always less than 100%, and attributed this reduction to pollinator
limitation, lack of pollinator attraction, overproduction of flowers
compensate
to for variations in resource availability (''bet-hedg-
We
or selective abortion of embryos. attempted to deter-
ing''),
mine whether reduced seed Carcx polymorpha was due
set in to
self-incompatibility, reduced pollen loads due to low air flows in
shaded or brushy or "bet-hedging'' and limited environ-
to
sites,
mental resources by conducting experiments with controlled pol-
and comparing
linations these results to open-pollinated plants
in several habitats.
The hypothesis was whether limited seed output
final tested
is
We
correlated with Carex polymorpha. compared
rarity in
fe-
C
common
and
cundity seed set with a species, vestita Willd.
C
Although
(section Carcx). not phylogenetically closely related,
vestita morphologically similar, occurs sympatrically, and pro-
is
comparison on
vides a useful congeneric to test hypotheses the
causes of of polymorpha.
rarity C.
MATERIALS AND METHODS
Study
Sites
Studies of Carex polymorpha were conducted in three popu-
Two
were Falmouth Cumberland
lations. located in Foreside,
County, Maine: the Borrow Pit an extensive area of former
site,
sand and gravel excavations with several vegetation types, and
km
Woods
Borrow
the less than 2 north of the Pit
site, site,
wooded and The was
undisturbed. third population located
in
Duxbury, Plymouth County, Massachusetts, and grew on sand
dikes of a former cranberry bog and adjacent woods.
in
Comparative o^ Carex were conducted pop-
studies vestita at a
which grew power
ulation in a line right-of-way adjacent to a
cemetery Stoughton, Norfolk County, Massachusetts.
in
Flowering Phenology
Each was weekly May, 1988 on
site visited in to collect data
The number
flowering phenology. of flowering shoots each of
in
was These were
five classes recorded. classes defined as not yet
1)
in flower, 2) in a female-only phase defined as having the stigmas
and
white exserted, in a hermaphroditic phase defined as having
3)
both stigmas and anthers exserted, in a male-only phase defined
4)
Dudley—
and Carex 271
Standley
1991]
and brown and and
as having anthers dehiscing stigmas withered,
flowering shoots that had ceased to flower. Additional obser-
5)
made Borrow numbers
vations were at the Pit site to assess of
flowering and vegetative shoots in consecutive 20-cm wide x
100-cm long quadrats along three parallel transects. Each of these
shaded
transects included areas of sand-vegetation edge, lightly
woods, and open sedge-dominated
areas.
Fecundity
Female
number
culms
mid-.uv yS8 trom
Maine
from
sample from an area in sun (area 100
full
1),
m
culms
from
collected from a population along a utility line easement in
both
Stoughton, Massachusetts. Seed (actual fecundity) in spe-
set
number
was assessed by determining the of mature achenes
cies
was
per flowering shoot. Percent seed set calculated as the percent
mature
of perigynia containing achenes.
Breeding System
The Carex polymorpha was
breeding system of investigated
Borrow
through experimental manipulation of plants at the Pit
May, The subpopulation occurs an open,
1989. selected in
site in
unshaded where would be expected be
seed to
relatively site set
This experiment was designed determine whether the low
high. to
seed observed in 1988 was due to either self-incompatibility
set
wooded
or to limited pollen dispersal in sites.
and
emasculated
Six treatments were used: emasculated, 2)
1)
emasculated, hand-pollinated with pollen
bagged, bagged,
3) 4)
from subpopulation, and bagged, hand-pollinated
a different
5)
from same subpopulation, and undisturbed
with pollen the
6)
controls. These treatments enabled us to determine whether plants
and
were apomictic, self-compatible, or self-incompatible, to iso-
Ten
any due to emasculation or bagging. replicates of
late effects
May
were done on
each treatment were used. All pollinations 21
removed
1989, and bags were ten days later, after pollen release
Rhodora
272
93
[Vol.
in the population had ceased, to allow normal achene develop-
The number
ment. unequal of replicates analyzed in the results
some
due to the death of shoots due to grazing or manipulation.
is
Plants were emasculated by manual removal of the terminal
sta-
minate spike or spikes prior emergence of stigmas, and were
to
bagged by enclosure of the entire flowering culm, prior to emer-
gence of stigmas, glassine photographic negative envelopes
in
(3
cm
X cm) which were Hand-pollination was
17 tied at the base.
accomplished by removal of staminate spike with dehiscent
a
anthers from a donor plant, and brushing the anthers of this spike
onto the exposed stigmas of the receptor plant until the stigmas
were visibly yellow. All the experimental culms were harvested
on 13 July 1989, and the total numbers of perigynia and mature
achenes were determined.
Morphology
Vegetative
Destructive sampling of rhizomes was performed the two
at
Woods
Maine m^ two Falmouth
quadrats: the
sites in six in
1
Woods
and
population designated three along the sand- veg-
2,
1
A
Borrow Borrow
etation edge at the Pit site designated Pit 1,2
wooded
and and one Borrow
in a partially area of the Pit site
3,
with a dense herbaceous layer of Carex polymorpha designated
Borrow Pit B. The purpose was to investigate patterns of rhizome
growth and shoot production. Data recorded for each inter-shoot
unit (consisting of one to several intemodes between scale-leaves)
cm
included the length of the unit and dry weight per the
o\^
number
rhizome. Data recorded for each node included the of
meristems produced and the developmental of each meristem
fate
Rhizome
(vegetative shoot, flowering shoot, rhizome). weight was
mm
determined 20 of excavated
for arbitrarily selected lengths
rhizomes 60°C
cut distally to the terminal living shoot, dried at
for 24 hours, and weighed to the nearest .0001 gram.
Vegetative morphology was examined by measuring
lengths
and widths of the longest leaf from arbitrarily selected shoots in
Woods
and Borrow Maine
the populations determine
Pit in to
whether canopy cover above-ground biomass production.
affects
Permanent
Plots
Shoot turnover was permanent
investigated in plots established
randomly
at selected intervals along a line transect through the
Dudley—
and C^r^x 273
Standley
1991]
longest axis of each population or subpopulation. Each permanent
cm cm
plot was 20 x 50 m^) and marked the four corners
at
(. 1
A
bamboo
by mapping frame
stakes inserted into the substrate.
plumb
with a transparent acrylic top and adjustable hanging hne
±
was used record shoot with an accuracy of cm.
to locations,
1
mapped
Shoot were May, and September
locations
in July, (the
early, middle, and late growing season) in 1988 and 1989 for the
Maine Permanent
populations. plots in the Massachusetts pop-
May
were sampled May, and September 1988 and
ulation in July
1989. These data were used determine recruitment and turn-
to
over rates of vegetative shoots within and between growing sea-
sons microhabitats.
in different
permanent were Borrow pop-
Six plots established the Pit
at
One
two was
ulation, three each along transects. transect placed
at the boundary between open sand and a vegetated area (transect
The
and were growing second was
A), plants in sand. transect
all
placed in an area with an open canopy (transect B) and a dense
herbaceous dominated by Carex polymorpha. Three
layer per-
Woods
manent
plots were established along a transect in the
Nine permanent were Dux-
population. plots established the
at
bury, Massachusetts Three plots were located along a transect
site.
on the top of a dike (transect A), three plots were in an area with
an open canopy and dense herbaceous dominated by
a layer C.
polymorpha (transect B), and three plots were located in pine
with dense canopy
forest a (transect C).
Canopy
Cover
Photographs were taken of the canopy by placing a camera with
mm
cm
above
a 28 wide-angle lens 10 the ground, facing
at
upwards. Photographs were taken when the canopy was fully ex-
panded, on 8 July 1988 in Maine and on 15 July 1988 in Mas-
A
was on
matrix of 100 evenly-spaced dots placed
sachusetts.
each photograph estimate the percent of canopy cover, which
to
At Borrow
correlated with light levels (Piper, 1989). the Pit
is
photographs of the canopy were taken within and at the edge
site,
wooded dominated by Carex polymorpha. At
of area
a partially
Woods
Falmouth photographs were taken
the several
at lo-
site,
cations within the population. At the Duxbury photos were
site,
wooded
where were
taken in the areas only vegetative shoots
present as well as in the open areas at the foot of the dike and
Rhodora
274
93
[Vol.
and
along the dike where both vegetative flowering shoots
trail
were
present.
RESULTS
Reproductive Biology
Flowering shoots comprise, on average, 1.5% of the total pop-
ulation of shoots in the Borrow Pit subpopulation sampled. Based
open
on our observations, this figure typical of populations in
is
shaded with well-developed canopy,
or slightly sites. In sites a
Woods
Falmouth comprise
such as the flowering shoots less
site,
1%
than of the In heavily shaded such as portions of
total. sites,
may
the Duxbury no flowering shoots develop.
site,
Plants o^ Carex polymorpha are protogynous. For an individual
shoot, the initial pistillate phase has a duration of less than a
week, the intermediate hermaphroditic phase has a duration of
one to two days, and the terminal staminate phase lasts from one
to several days. Although dichogamous, the overlap in flowering
permits
potentially self-pollination to occur.
among
and
Plants within populations exhibit considerable
Maine Borrow
asynchrony in flowering. At the sites, the Pit pop-
Woods
The
ulation initiated flowering earlier than the population.
Borrow population was predominantly the hermaphroditic
Pit in
May Woods
phase on 16 1988, which date the population had
at
A
not begun to flower. week on 24 May, flowering shoots
later,
at the Borrow Pit had ceased flowering or were in their terminal
Woods
were
staminate stage while shoots at the population in
all
Woods
showed
a staminate phase. This population a high degree
of synchrony and completed the entire flowering sequence in 8
days. At the Massachusetts population, flowering of different sub-
populations was also asynchronous, and flowering occurred over
12-day period from 8-19 May. Achenes were mature both
a in
Maine and Massachusetts populations by 23 approximately
July,
weeks had
eight after flowering ceased.
The number number
of pistillate spikes, as well as the of peri-
among
gynia produced per flowering shoot, varied subpopulations
Carex polymorpha Borrow
of the shoots area had,
at Pit in 3
site:
most, one spike and on average 6 perigynia per spike,
at pistillate
1
and had one and
while shoots in areas 2 at least pistillate spike
1
on average 32-40 perigynia per shoot (Table This difference
1).
Dudley—
Standley and Carex 275
1991]
C
Table Female flower and production of Carex polymorpha and
fruit
1.
mean ±
veslita (data are the SD).
1
No.
Pistillate
%
Population Spikes No. Perigynia No. Achenes Seed
Set
Borrow ± ± ± ±
Pit 1.3 0.4 40.1 17.0 30.1 15.5 72.7 20.8
(1)
Borrow ± ± ± ±
Pit 1.4 0.5 32.1 11.7* 1.2 1.7* 4.5 6.4
(2)
Borrow ± ± 7.1* ± ±
Pit 1,0 0.0 16.3 1.2 1.9* 7.4 0.1
(3)
± ± ± ±
C. vestita 1.9 0.7 94.4 37.5 6.4 6.3 6.8 6.2
Means P <
are not significantly dilTercnt at in Student's comparisons;
all
1 /
.
means
other were
significantly different.
among
subpopulations in potential fecundity appears to be cor-
C
related with shading and canopy closure. Shoots of vestita
tended to have two pistillate spikes and, on average, 95 perigynia
(Table
1).
number
Actual fecundity, measured as the of achenes and the
percentage of perigynia which produced mature achenes, varied
among
Carex polymorpha and
subpopulations o^
significantly be-
The
tween two unshaded
the species (Table open, relatively
1).
subpopulation of polymorpha Borrow had
C. at the Pit site a
1
72%
seed of and produced on average 30 achenes per
set pistillate
This number from two more
spike. significantly different the
is
shaded Maine subpopulations which produced fewer than
(2, 3),
two achenes per spike and had seed of than 10%. All
sets less
C
polymorpha from
populations of
C. differed significantly ves-
which produced from 0-25 mature achenes per flowering
tita,
shoot with an average seed of than 7%.
set less
Mature achenes were obtained experimental
in pollination
all
treatments (Table The highest percent seed was observed
set
2).
Table Achene production breeding system experiment (mean ± SD)
2. in
1
(See text for further explanation.)
%
Treatment* n Perigynia Achenes Seed Set
± ± 78%
52 25 42 22
9
1
± ± 30%
2 8 58 20 14 13
22+10
± 55%
43
3 7 17
± ± 62%
4 9 55 18 34 13
+
± 70%
44
5 7 18 31 18
37+17
± 79%
46 22
6 7
= = ^
* emasculated, open-pollinated; 2 emasculated and bagged; 3 selfed
1
= =
(bagged); 4 outcrossed (emasculated, hand-pollinated, bagged); 5 hand-pol-
=
linated (emasculated, hand-polhnated); 6 control.
Rhodora
276 93
[Vol.
and These
for the open-pollinated plants in treatments 5 6.
1,
seed rates (> 70%) arc comparable to those found for plants
set
open demonstrating that emasculation or hand-pol-
habitats,
in
The somewhat
have no discernablc on seed
lination effects set.
and show no
lower seed figures for treatments 3 4 difference
set
same
between donor pollen from the plant or a different clone,
The
was somewhat by
limited bagging.
but suggest that seed set
which were expected
low seed set for treatment 2, in plants to set
no and have seed apomictic,
seed sexual to a significant set if
if
we
However, found although spikes are funda-
puzzling. that
is
developed
mentally unisexual, the majority of pistillate spikes a
which were not
few inconspicuous staminate flowers at their tip
The
noticed and therefore not removed by emasculation. presence
of some pollen within the pollen exclusion bags in treatment 2
from these few anthers could explain the low level of seed set in
experiment apomixis
treatment testing for apomixis. This for
this
thus not conclusive, but results are consistent with the hy-
is
compat
mictic.
Morphology
Vegetative
Growth Carex polymorpha sympodial,
the clonal species
in is
The
and occurs in the following sequence. apical mcristem of a
rhizome turns upward and develops into a vegetative shoot which
persists for a single growing season. During the growing season,
meristcms form the base of shoot; these meristems
axillary at this
may
develop into elongate rhizomes which initiate further veg-
may
rhizomes
develop ascending
etative spread, or into short
which form either vegetative or flowering shoots. Individual leafy
shoots persist for only a single growing season. This form of
sympodial growth produces a pattern of either single, isolated
may
shoots meristem growth of elongate rhizomes, or
if all is
most meristem
produce a pattern of tightly clustered shoots
if
growth of ascending rhizomes.
short,
is
The rhizome growth was quad-
pattern of investigated in the 6
were By rhizomes
rats that excavated. tracing for their entire
we found few shoots
length these quadrats, that relatively in
in
same Rhizomes
any given square meter belonged to the clone.
are capable of continued growth for several meters, and rhizomes
and
from several different directions converge intermingle in a
and Dudley— Carex 211
Standley
1991]
num-
Table Comparison rhizome inter-shoot unit lengths and meristcm
ol
3.
ber among samples of Carex polyinorpha in Maine.
Mean
Mean Rhizome Number Canopy
Quad- of
SEM
n Length (cm) ± Meristems Cover
Site rat
Woods 144 5.078= 0.484 1.243 b closed
1
2 370 6.304= 0.389 1.372^ closed
A
open
Borrow 22 13.855^ .b 2.445 1.567^
Pit
1
2 38 15.850^ 1.752 2.721^ open
open
86 11.506" 1.418 2,372^
3
Borrow B 74 3.920= 0.393 1.107^ closed
Pit
1
Studenl-Newman-Keurs
^^-'^ Differences between means were assessed using a
ANOVA
among means
an of comparisons by Differences
posteriori lest in site.
P < Means same
with different group letters were significant at .0001. with the
SEM =
were not significantly different. standard error of the mean.
letter
among
This growth pattern indicates that competition
single area.
may
genets be occurring at a high level in populations
different
of Carex polymorpha that consist of more than one genet. Intact
systems
based on our observations
pattern,
may
remain
ramets
rhizome
node
long as 10 years, based on the observation that a single is
produced per year at this site.
among
Rhizome
inter-shoot unit lengths differed significantly
when
and were grouped according to
(Table
these sites
sites 3)
Woods
Rhizome and
canopy inter-shoot lengths in the
types.
cm cm
Borrow Average
an open sand quadrat the Pit inter-
in at site.
cm
cm
P < F
variance showed this difference to be significant at .0001,
92.68.
Woods
rhizome segments between the
differed
md
The average rhizome dry weight
quadrats.
cm
Woods
from
Dlants in the
=
Student's (df 44) found this difference to be significant
?-test
g.
P =
was
<
atP lower of
1.7939 significance level
(the
.1
.1,
t
amount
