A Re-evaluation of Isoetes savatieri Franchet in Argentina and Chile

11 Pages·2003·5.8 MB·English

by  R James Hickey

American
Fern Journal 93(3):126-136
(2003)
A
Re-evaluation of Isoetes savatieri Franchet
in
and
Argentina
Chile
James Hickey
R.
Botany Department, Miami OH, 45056
University, Oxford,
Macluf
Cecelia
Catedra de Palinologia, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La
Plata Paseo del Bosques s/n, 1900 La Plata, Argentina
W.
Carl Taylor
Botany Department, Milwaukee Museum, WI
Public Milwaukee,
—
Abstract.
Isoetes savatieri has traditionally been interpreted being uniform
as a aquatic ranging
from the southernmost regions of South America to the central Andes of Chile and Argentina. An
examination of herbarium material supports the recognition of two taxa, a southern savatieri and
/.
more
a northern chubutiana, from central Chile and Argentina. The taxon hexaploid and
/. latter
is
new
described here as a species. The morphology
of these species suggest that they are sister
species resulting from divergence following a polyploidy event. These species, and several other
species pairs, provide the best and, only examples
to date, of allopatric divergence in polyploid
Isoetes.
Isoetes a nearly cosmopolitan genus
is of aquatic to sub-aquatic perennial
lycopsids. Estimates number
of species has ranged from 60
1922)
(Pfeiffer, to
150 (Tryon & Tryon, Recent work
1982). systematic North America
in
(e.g.,
Brunton &
&
Britton, 1997, 1998; Caplen Werth, 2000, 2000b) and South
America
(Small & Hickey,
2001; Hickey, however, even
1994), indicates that
150 likely to be an underestimate. The number
is actual worldwide
of species
probably
closer There
is to 350. are several reasons
for this large disparity.
Despite a long history of systematic and
morphological genus
the
interest,
is
poorly
collected (Hickey and
et al., 1989) only sporadically studied. Aside
th
from
the classic 19 Century works of Baker (1880) and Motelay & Vendryes
(1882) there has only been one modern
systematic treatment of the genus
worldwide
monograph
(Pfeiffer, 1922).
Pfeiffer's stands as the classic treatment
of the genus number
despite
a
of significant but unavoidable Most
flaws.
among
significant these
the lack of adequate
is Neotropical
collections
examined
during
the study. working
Pfeiffer, out of the Missouri Botanical
Garden, MO
relied almost exclusively on specimens
housed GH, and
US.
at F,
She did not examine many
the important
collections held Europe and
in Latin
America
and, was
as a result, unable develop
to a
full
diversity of the genus
as occurs South
in America.
it
South America
appears
be
to the center of both morphological and
taxonomic
diversity
for Isoetes (Hickey, The
1990). richness of the South
American was
flora evidenced work
first in the Weber
of Ulrich
(1922). In
a revision of the South American
he
species, recognized 18 which
taxa, 11 of
^
he ™* ™™^i
described new. ™*;™i„
as Weber's work, whilp rprtfunW
n «.
—
HICKEY ET RE
AL.:
127
accurate, stands in contrast to the work of Pfeiffer which recognized only seven
species for all of South America. The next significant work on South American
was
Isoetes that of Fuchs-Eckert (1982) in which he recognizes 75 species. In
an overly conservative work, Hickey recognized 47 South American
(1985)
species but has since accepted considerably more (Hickey, 1994; Small &
Hickey,
2001).
This paper adds to our knowledge of the genus in South America by
new
new
describing a species, allied to Isoetes savatieri Franchet. This taxon
was
recognized by was
first as distinctive Fuchs-Eckert (1982) but never
We
validly published. compare both species and continues a discussion
(Hickey on
et 1989) speciation in the genus.
al.,
Isoetes savatieri Franchet, Bull. Soc. Bot. France 31:395. 1884. Calamaria
PL
savatieri (Franchet) Kuntze, Rev. Gen. 1891-1893.
2:828. Isoetes lechleri
Gomez,
var. savatieri (Franchet) L. D. Brenesia 18:5. 1980. Type: Argentina,
Puerto Bueno, 15 Feb 1877, Savatier s.n. (Holotype: P), ex char. Figs. 1-3.
mm mm
Corm somewhat
globose to laterally elongate, 9-12 wide, 8-10 high,
2-lobed; roots dichotomous, arising synchronously within the continuous
circumbasal Leaves 6-22, 42-163
fossa. stiffly erect or slightly recurved, brittle,
mm mm
mm
7-14 wide wide mid
long, at the base, 1.8-5.0 at length; alae
hyaline and chartaceous proximally, dark green and membranaceous
distally,
mm mm
1.0-3.5 wide the sporangium, 12-65 long (extending up 29-65%
at for
of the leaf length), each apex obtuse; subula terete, dark green, the apex short
acuminate; fibrous bundles absent; stomates absent; scale leaves and
phyllopodia Sporangium
absent. circular to elliptic, hyaline, tan, concolorous,
mm mm
Velum
3.0-9.5 long, 3.5-6.2 wide, basal. incomplete, extending
mm
down
(0.5)1.5-2.5 from the top of the sporangium. Ligule deltate to widely
mm
ovate, hastate-auriculate, delicate and ephemeral, 2.5-3.0 long, 1.8-3.3
mm
wide. Labium inconspicuous, represented by a low, entire or scalloped
membranaceous, 40-60 70-100
ridge, light green, high, |im wide.
(.im
=
Megaspores white to off-white, frequently lustrous, 370-580 (x 479) fim in
diameter, rugulate or rarely tuberculate, girdle sparsely ornamented; equatorial
and proximal ridges straight, distinct, as high as broad. Microspores light gray,
= =
Chromosome
35.0-46.3 25.0-33.8 wide,
(x 39) Jim long, (x 29) |im laevigate.
number
unknown.
—
Endemic low around Fuego
Distribution. to the coastal regions Tierra del in
Chile.
Ecology.
th
found below 200 m. The plant apparently an obligate aquatic, inhabiting the
is
shallows of streams and lake margins. Vegetative reproduction frequent and
is
gemmae.
accomplished by the production of cortical This species produces
is
megaspores and microspores January through
April.
Isoetes savatieri characterized by an acuminate leaf apex, a hastate-
is
auriculate ligule, a partial velum, and a minute labium. differs from
It
/.
AMERICAN FERN VOLUME NUMBER
128 JOURNAL:
93
3 (2003)
SEM
Figs. 1-6. images of Isoetes megaspores and microspores. view
1. Distal of savatieri
J.
megaspore
(Borge NY). view
s.n., 2. Equatorial of savatieri microspore {Borge NY).
/. s.n., 3.
Proximal view megaspore
of of savatieri showing tetraradiate proximal
ridges (Borge NY).
/. s.n., 4.
Distal views of chubutiana microspores showing broad
I. echinate surface markings [Taylor 6168,
LP). Equatorial view of megaspore from chubutiana
5. (Taylor 6168, Proximafview
LP).
/. 6. of/.
chubutiana microspore showing monolete
suture (Taylor 6168, LP). Bars in figs. 1, 3, and 5 are
100am; those in 4 and 6 are lOum.
2,
chubutiana
in leaf shape, in particular leaf width and apex shape, and
to
mor
with acumen,
a distinct whereas chubutiana
generally has more
a tapering
/.
apex and
obvious acumen.
less Isoetes savatieri has broad,
short leaves; the
mm,
range in leaf width 2-5 with mean and mean mm.
is a of The width/
3 leaf
ni^N^Y £1 Kt-tVALUAllU.N Ut SUt IbS SAvAIltiHl
/\L.: 129
1
Table 1. Comparison of traits in Isoetes savatieri and chubutiana.
/.
savatieri chubutiana
I.
I.
= =
Leaf width (mm)
1.8-5.0 1.5-2.2
(x 3) (x 1.7)
= =
Leaf width/length 9-47 19-98
ratio (x 24) (x 62)
Leaf apex shape blunt tapering
Acumen
weak
distinct
Alae development:
%
29-65
of leaf length 18-30[45]
Alae apex shape obtuse
attenuate
Megaspore
surface rugulate to rarely sparsely densely
to
morphology
tuberculate
rugulate, to cristate, to
reticulate
= =
Megaspore 370-580 460-750
size (urn) (x 479) (x 595)
Microspore
surface laevigate sparsely densely
to
morphology
echinate; the spines narrow
broad based
to
= =
Microspore length (um) 35.0-46.3 33.8-41.3
(x 39) (x 39)
= =
Microspore width (um) 25.0-33.8 26.2-33.8
(x 29) (x 30)
mean
length ratio ranges from 9 to 47 with a of 24. In cubutiana, the leaves
I.
mm mm
mean
are narrower; leaf width ranges from 1.5-2.1 with a of 1.7 and
mode mm.
The mean
a of 1.5 leaf length/width ratio ranges from 19 to 98 with a
value of 62.
Megaspores some Donat
of savatieri are rugulate except in individuals of
/.
Some
380 where the spores are tuberculate. of the spores of this collection have
the tubercles confluent to form short muri, approaching a rugulate condition.
The more
megaspores chubutiana are variable; they range from sparsely
of/, to
densely and Although
rugulate to cristate finally to reticulate. there
is
number
tendency produce and
a in the latter species to a greater of leaves to
have larger megaspores, these differences are not reliable enough for
identification purposes. The microspores of savatieri are laevigate, whereas
J.
in chubutiana they are sparsely to densely echinate. In all other characters
J.
two
the taxa are virtually indistinguishable. Isoetes savatieri geographically
is
separated from chubutiana by some 1000 km.
I.
same
The megaspores of Isoetes savatieri are about the size as those of
same
the hexaploid Isoetes chubutiana suggesting they are the ploidy level
&
(Small Hickey, 2001; Troia, 2001).
—
Mar
Specimens Examined. CHILE. Magallanas: Laguna Maravilla, in altitudine bimetrali, 22 1899.
Mar
Borge s.n. (GH, NY, US); Lago del Toro (L. Maravilla), La Peninsula. 10 1941, Santesson 1747
Region Riesco; 22 Mar 1931, Donat 380 (BM, F, GH, LIL, M, NY, SGO, U); en charcos con
(S);
gramineas, Jun 1972, Gomez PAT3803 (CR); Isla Desolacion, Puerto Angosto, 6 Apr 1896. Dusen
705 MO, UPS[2]); SE of Caleta, Josefina (Onaisin) on rd to Rio Chico, 53°32'S, 69°09'W.
(LIL, 0, S,
Nov Moore 2423 Laguna
Bolax-Empetrum heath near lake, 11 1971, (H, HIP); "El Parrilar;"
sumergida +/- 10 cm bajo nivel inferior de las aguas, entre piedros, suelo arenoarcilloso, 7 Feb
a
1971, Pisano 2938 (HIP); arrojado a la playa por las olas, 26 Jan 1973, Pisano 3871a (HIP); Isla
Rennel Canal Smyth, 74°12'S, 51°54'W, river bottom, rocky bottom w/ ferric accumulation,
Norte,
submerged +/- m, Transecta Botdnica de Patagonia Austral 1151 (HIP-2); consolidated organic
0.3
mud Transecta Botdnica de Patagonia Austral 1205 (HIP).
rich in iron,
AMERICAN FERN VOLUME NUMBER
130 JOURNAL:
93
3 (2003)
Figs. 7-10. Isoetes chubutiana. Proximal and view
7. equatorial of microspores [Taylor 6171, LP);
=
scale bar 10 nm. Equatorial view of megaspore with smooth and
8. girdle retate surface markings
= =
(Taylor 6171, LP); bar 100 Root squash 2n
|im. 9. tip of 66 [Taylor 6171, MIL). Root
10. tip
=
squash In 66
of (Taylor 6168, MIL).
Isoetes chubutiana Hickey, Macluf & W. nov.—
C. Taylor, spec, Type:
Meyer
4-10
Wetensch
C85:255.
1982.
Meyeri Fuchs, nom.
nud., Proc. Kon. Ned. Akad. Wetensch.
C85:231,
/. 241,
Based
242, 255. 1982. on: Argentina; Gob. Rio Negro, Cascado
Rio
del
Manso,
30 Jan 1945, based on Meyer 8238
{LIU).
Cormus mm
globosus usque
lateraliter elongatus, 4-23 3-10
bilobatus,
latus,
mm
i
9-30
HICKEY ET RE-EVALUATION OF
AL.: ISOETES SAVATIERI
131
and
Distribution of Isoetes savatieri (circles) chubutiana (diamonds)
Fig. 11.
/.
AMERICAN VOLUME NUMBER
FERN JOURNAL:
132 93
3 (2003)
mm mm
medio
basi lata, 1.5— 2.2[3.0] lata; alae proximale hyalinae et chart-
mm
membranaceae, 11-55
aceae, distale atrovirides longae (18—30[45]% per
et
longitudinem ascendentes), apicibus subula
foliae attenuatis; teres, atroviridis,
squamae
apice longe acuminato; fasciculi fibrosi peripheric!, stomata, et
phylllopodia Sporangium usque hyalinum,
absentia. circulare ellipticum,
mm mm
concolor, 2.8—6.7 longum, 2.8-5.7 latum, Velum incompletum,
basale.
mm.
descendens ad 0.7-2.7 Ligula deltata usque ovata, cordata usque
late
mm mm
hastata, viridi-nigra, tenella atque fugax, 1.5-3.0-1- 1.7-2.3
elata, lata.
Labium inconspicuum usque absens. Megasporae albae usque cretaceae, saepe
=
460-750
nitidae, (x 595) (im diametro, rugulosae usque rugulosae-cristatae
zona non usque
vel reticulatae; dissimilis laevis; cristae aequatoriae proximal-
quam
non
esque rectae, distinctae, altiores latae. Microsporae cinereae usque
= =
brunneae, 33.8-41.3 (x 39) |im longae, 26.2-33.8 (x 30) jim latae, sparse
=
usque dense echinatae. Chromosomatum numerus 2n
66.
mm mm
Corm globose somewhat elongate 4-23 wide, 3-10
to laterally, high,
2-lobed; roots, dichotomous, arising synchronously within the continuous
circumbasal fossa. Leaves 9-30, erect or more rarely recurved
stiffly distally,
mm mm mm
brittle, 40-280 long, 6.0-9.0 wide at the base, 1.5-2.2(3.0) wide at
mid
and
length; alae hyaline chartaceous proximally, dark green and
mm mm
membranaceous distally, 1.2-3.0 wide at the sporangium, 11-55 long
up
(extending for 18-30(45)% of the leaf length), each apex attenuate; subula
terete, dark green, the apex long acuminate; fibrous bundles absent; stomates
absent; scale leaves and phyllopdia Sporangium
absent. circular to elliptical,
mm mm
hyaline, tan, concolorous, 2.8-6.7 long, 2.8-5.7 wide, Velum
basal.
mm
down
incomplete, extending 0.7-2.7 from the top of the sporangium.
Ligule deltate to widely ovate, chordate to hastate, black, delicate, ephemeral,
mm
mm
1.5-3.0+ high, 1.7-2.3 wide. Labium inconspicuous
absent.
to
=
Megaspores
white white, 460-750
to off often lustrous, (x 595) |im in
diameter,
rugulate,
rugulate-cristate, to reticulate, girdle undifferentiated to
smooth; equatorial and proximal
ridges straight, distinct, as high as broad.
= =
Microspores light grey to dark brown, 33.8-41.3 (x 39) (am long, 26.2-33.8 (x
=
30) |im wide, sparsely to densely echinate. Chromosome number 2n
66.
—
Endemic Andes
Distribution. to the central of Chile and Argentina.
—
m
Ecology. Isoetes chubutiana grows at elevations of 750 to 1300 as
submerged
a aquatic in the shallows of streams and from
lakes. Collections
November, March
January, February, and April have megaspores and micro-
May
spores. Collections from have only microspores. The absence
of
from
collections the rest of the year precludes further statements about yearly
phenology. Isoetes chubutiana, number and
like a of species of the central
south central Andes, reproduces asexually by the production of cortical
gemmae.
In technical characters of the sporangium, velum, and chubutiana
ligule,
is
J.
from
indistinguishable savatieri. can be distinguished from however by
/. It it
leaf form, as described under savatieri, and to a lesser extent by megaspore
/.
morphology.
HICKEY ET RE-EVALUATION OF ISOETES SAVATIERI
AL.: 133
The names valdiviensis and meyeri were published by Fuchs-Eckert
/. I.
without an enumeration South
(1982) latin or english descriptions as part of of
American Diem
species. In addition, 1105 (GH) annotated as the type of the
is
name
unpublished "herbarium" Isoetes chilensis. This plant and those
annotated Meyeri and accommodated within
as valdiviensis are best
/. /. /.
chubutiana.
Megaspore and microspore ornamentations extremely
are variable in this
common
otherwise uniform taxon. The most megaspore type in the southern
more
portion of the range rugulate while the northerly collections are
is
South American with
typically reticulate. In other species reticulate
all
megaspore ornamentation the microspores are laevigate. In this species,
however, the microspores generally have an underlying or dominant echinate
surface pattern. The presence of reticulate megaspores in this species provides
morphology and
additional evidence of convergence in spore seriously
undermines the recognition of a Section Terrestres [sensu Fuchs, 1982;
Reticulatae of Pfeiffer, 1922), a section currently based almost exclusively on
the presence of reticulate megaspores.
Apr Maldonado
Paratypes.—CHILE. Aysen: Lago Gral, Paz, 15 1943, 288 (LP);
(CONC); Ventisquero
Chile chico, a orillas del algo, 3 Dec. 1946, Castillo s.n.
24-25 Mar 1967, Seki 581II {CONC). Llanquihue: La Turbina, Payne, en
Soler,
Rio Payne, despues del Salto Chico, 22 Feb 1974, Pisano 4304 (HIP);
orillas del
Mar
Puerto Varas, Puella, Rigi, 125 m, 41°06'S, 72°02'W, 1967, Zollitsch 298
Rupanco, poca profundidad m)
(CONC). Osorno: de hidrofito crece a
Isla (1
orillas, 15 Mar 1978, Godoy s.n. (SGO); Isla de Rupanco, aquatica, se desarrola
almde
Mar Godoy
profundidad en lago Rupanco, 7 1979, 3 (SGO); Isla de
el
m
Rupanco, acuatica, de desarrolla a de profundidad y en orillas sobre arena,
1
Mar 1979, Godoy (SGO); Lago Rupanco, Rio Pecaderos, 8 Dec 1945,
7 s.n.
Rudolph 43,676 (CONC); Lago Puyehue, (Isla Fresia), costa en sur y vuelta (en
Feb Heins 1744 (CONC).
1954, Levi
el agua), 5
ARGENTINA. Neuquen: Depto. Minas, Lagunas Epu-Lauquen, Aduana
cm
sumergida en de lagunas, +/- 50 de profundidad, 1300
Vieja, las orillas las
m, 15 Jan 1964, Boelcke et al. 10871 (BAA, SI); extremo norte de la laguna
Varvarco Campos, orillas, 2 Feb 1970, Boelcke et al. 14336 (BAA), 14337 (MU,
Puerto Manzano, 13 Feb 1934, Burkart 6499 (BM, SI); Lago Espejo y
SI);
m
Apr Meier Lago
correntoso, profundidad, 16 01, s.n. (LP); Lacar, playa
1
&
San Martin de Los Andes, Mar 1966, Burkart Troncoso 26447
cerca a 1 (SI,
niedrigem wasserstand beinahe ausserhalb des Wassers,
UC); Lago Totoral, bei
m
Diem 3379 M, NY); Quetrihue, en aguas
900 m, 22 Feb 1970, (L, tranquilas, 1
May Diem 646 Punta Quethihue, en
playas
bajo agua, 30 1942, (SI);
el
Mar
formando comunidades puras numerosas, 770 m, 8 1959, de
inundadas, y
m
Lago Nahuel Huapi: Puerto 1-2 de
2167 Rio Negro: Pafiuelo, a
Sota
la (LIL).
Feb Burkart 6548 Puerto Feb
profundidad en aguas, 15 1934, (SI); Pafiuelo,
las
Hauman Parque Nacional Nahuel Huapi, E side of Lago
1911, (LIL);
1
humus among
anchored sandy submerged
in rocks,
Guillelmo, plants firmly
Mar
0.75-1.0 m, 840 m, 41°22.3'S, 71°29.7'W, 17 2001, Taylor 6168 (LP,
elev.
134 FERN JOURNAL
MIL); Parque Nacional Nahuel Huapi, S Lago
side of Mascardi, plants firmly
anchored sandy humus among
in rocks, submerged 0.75-1.0 m,
41°21.35S,
m
71°34.3'W, 822 m, Mar
17 2001, Taylor 6171 (LP, MIL); Lago 1-2
Frias, bajo
agua en
extensas colonias enterreno arcuosa-arculloso, 800 m, Nov
1947,
1
Diem
1105 Cascado
(GH). del Rio Manso, 30 Jan 1945, Meyer 8238
(LIL).
Chubut: Lago
Futalaufquen,
14 Jan 1945, Castellanos 114242 (AA); Lago
Futalaufquen, Reserva Nacional de Mar
los Alerces, 27 1949, Pedersen 302
(C,
Lago Verde, Parque
S); Nac. Los Alerces, sumergida en no, 25 Feb
el 1950,
Soraimo 4287
(BAA).
An
interesting aspect of both species the sporadic occurrence
is of irregular
Donat
spores. In 380 {I. savatieri) the megaspores show a high degree of size
dimorphism
whereas the microspores show 70%
ca. spore abortion. Borge
s.n.
savatieri) contains megaspores with
[I. occasional tetraradiate meiotic
scars
(Fig. often an indication of meiotic shows 1-2%
3), irregularity, but only
microspore
abortion. In I. chubutiana, a plant from Castellanos 11424 has very
irregular megaspores, both and
in size shape, yet has normal
perfectly
microspores. Such
situations are frequent
in other species of the genus,
for
Muerte
Weber
More
of
Brazil.
Mett
complex
1994). In that both
of the currently recognized members,
lechleri
/.
and T* herzogii" * WT teT b1 er *
/.
Memb
of the complex
lechleri
are notorious
/. for their high megaspore
rate of
abnormalities, reminiscent
of meiotic Hickey
irregularity. hypothesized
(1994)
phenomenon
that was
this
the
result of polyploidy followed by
differential
gene
silencing and, through
subsequent
out-crossing, the accumulation
of
reciprocal gene
silencings (Werth and Windham,
The
1991). spore abortion
seen and
in savatieri chubutiana
J. likely be
/. is to of similar
origin.
The
hexaploid
chubutiana
probably
the
is result of through
/. stabilization
polyploidy
of a sterile triploid, with the
triploid springing from
a hybridization
event between A
a tetraploid and number
a diploid.
of features suggest that the
tetraploid parent was member
a
of the lechleri complex. That complex and
I. the
members
of the savatieri complex gemma
share
/. cortical production and
a turgidly
brittle leaf habit, both unusual
features in the genus. In addition, they
share
a similar
habit, similar spore morphology, and
have
nearly contiguous
The
ranges.
rugulate herzogii more
/. is likely involved than the
laevigate
/.
The
lechleri. diploid parent might be
Weber
boliviensis and
of Bolivia Peru
/. or
alcalophila Halloy
/. (interpreted here as including escondidensis
Halloy) of
/.
Web
th
complex, but chromosome
number
its not known.
yet
is
Taylor and Hickey
(1992) discussed mechanisms
the
of speciation
in Isoetes
and
have noted two
predominant
The
patterns.
first is characteristic of lowland
diploid and
taxa
involves
allopatric divergence. The second
allopolyploidy.
is
The common
latter
is in "social"
species,
typically
aquatics of temperate or
HICKEY
135
upland
tropical regions. Little attention has been given to the origin of lowland
polyploids nor has convincing evidence been provided divergence
for
subsequent polyplod Perhaps example
to a event. the best potential of
was
polyploid divergence be found Engelm. complex
to in the Isoetes riparia of
North America
eastern This assemblage
(Proctor, 1949). of tetraploids includes
and
several specific subspecific segregates that have variously been elevated in
rank subsumed The two known
or since their initial descriptions. best
segregates are saccharata Engelm. and canadensis (Engelm.) A. A. Eaton.
/. /.
shown
Recently, however, has been complex
that this riparia
it is
/.
and number
polyphyletic
consists of a of similar but phylogenetically
distinct
some &
polyploids sharing but not ancestors (Caplen Werth, 2000a, 2000b).
all
In South America, there are several good candidates for divergence following
polyploidy. Within the Isoetes lechleri complex, there a tremendous amount
is
and number
of inter-populational differentiation, a of specific segregates have
been proposed (Fuchs-Eckert, 1982; Hickey, Hickey argued
1985). (1994) that
most accommodated more
of these segregates are best in a inclusive lechleri.
J.
However, the populations from central and southern Bolivia form a cohesive
assemblage enough from
distinct the northerly lechleri to be recognized at
/.
the specific level as herzogii. Similarities in morphology, identical
/.
chromosome gemmae
number, and and
spore abortion, cortical in lechleri
/.
herzogii argue strongly for a divergent rather than an independent origin for
J.
these tetraploids. Likewise, similarity in morphology, spore ornamentation,
spore and geography supports an allopatric-divergence model the
size, for
/.
savatieri-chubutiana polyploid pair. These examples then represent the best
evidence to date for allopatric speciation in polyploid Isoetes.
The combination of a high incidence of polyploidy in the genus (58.1%,
Troia, 2001) and the rarity of allopatric polyploid speciation surprising.
is
It
suggests that Isoetes, which appears to date back to the earliest Triassic
(Grauvogel-Stamm and Lugardon, 2001), as Isoetites, has persisted through
geologic time primarily as basic diploids. further suggests that either
It
polypoidy a relatively recent process in the genus and/or that polyploids are
is
ephemeral taxa that position themselves temporarily in vacant niches. Support
modern
models comes from
for both of these the distribution of polyploids:
most polyploids being found in fairly recent habitats such as temperate,
by such high paramos
glaciated regions, areas affected glaciations, or altitude
and These models are also supported by allozyme studies: polyploid
lakes.
show
and no evidence
Isoetes appear to retain fixed heterozygosity little or of
(Caplen and Werth, 2000a, 2000b), suggesting
extensive diploidization
The preponderance of data concerning Isoetes
relatively recent origins.
evolution suggest that polyploids are of little consequence from a divergence
way
do evolve by of additional rounds of polyploidy.
standpoint, but certainly
Morphological, geographic and cytological data from the savatieri-I.
J.
provide an arena whether
chubutiana and the Iechleri-I. herzogii pairs to test
/.
model divergence following polyploidy,
of speciation,
there a third
is
such lowland
Other wide-ranging tetraploids as the
occurring in the genus.
Maxon & Morton, which ranges from Central America
panamensis C. V. to
/.