Table Of ContentRHODORA,
No. 287-293, 1994
Vol. 96, 887, pp.
NEW
A TRI-HYBRID LYCOPOD,
SABINIFOLWM
DIPHASIASTRUM DIGITATUM
x
Arthur Oilman
V.
ABSTRACT
A
putative hybrid Diphasiastrum (Lycopodiaceae) described from
tri-specific is
a collection in northern Vermont and is figured in a line drawing. The hybrid is
morphologically intermediate between probable parents, D, digitatum and D.
its
xsabinifolium. This the flat-branched hybrid lycopod believed to involve
is first
three parental genomes. In light of its limited occurrence (a single clone), it is not
given an
epithet.
genome
Key Words: Diphasiastrum {Lycopod am), hybrid, analysis, species con-
i
Vermont
cept,
INTRODUCTION
and
Five hybrids, of the '"flat-branched"
species, at least five
known North
lycopods {Diphasiastrum Holub) are in northeastern
America (Table The taxonomy of this group has to date relied
1).
almost on morphology. Hybrids generally display char-
entirely
and
between
acters intermediate their parents, are usually distin-
and herbarium on morphological grounds
guishable in the field
work ah North
(Wilce, 1965). Cytological has indicated that
American and chromosome number 2n
species hybrids share a
^
46 Wagner, with apparent normal pairing behavior
(F. S. 992),
1
and spore formation in the hybrids (the plant described here
produces well-formed spores). Additionally, the difficulty of ger-
minating spores and growing the resulting plants has so
in vitro
experiments Diphasiastrum,
precluded crossing in
far artificial
and genus whole has not been analyzed on the basis of
the as a
DNA. On
isozymes or morphological grounds, Wilce (1965) de-
termined D, xsabinifolium, which had long been considered a
x treatment
be the hybrid D, sitchense tristachyum, a
species, to
Cody and
which has gained acceptance 1979; Britton,
(Beitel,
Wagner and Except D, which
1989; Beitel, 1993). for xissleri, is
known from and complanatum
in our area a single collection, D.
may sometimes
X digitatum, which be quite rare, the hybrids are
common W.
(Cody and H. Wagner,
Britton, 1989; pers.
locally
comm.), and D. xsabinifolium sufficiently so to be regarded as a
The Wagner,
nothospecies. hybrids appear to be fertile (F. S.
no hybrid progeny or backcrosses with parent species
1992), yet
287
Rhodora
288
96
[Vol.
Table Species and hybrids of Diphlaslruni northeastern North America
in
1.
-
2n
(all 46).
Species
Holub
D. digitatum (DiU.)
Holub
D.
co)}ipIanatUfi} (L.)
Holub
D. iristachyum (Pursh)
Holub
D. sitchcnsc {Ku^r.)
Holub
D. alpinuni
(L.)
Hybrids
Holuh x
D. xsahinifolluni (Willd.) {sitchcnse iristachyum)
Holuh
D. xhabercri (House) {ciigilatum x iristachyum)
D. complanatum x digitalum
D. xzcillcri {Rouy) Holub (complanalum x iristachyum)
D. X {Rouy) Holuh (alpinum x trislachyum)
issleri
have been described. This paper discusses a new hybrid, D. dig-
X known
itation sahinifo/ium, present from
at a single station in
northern Vermont. known
the hybrid have hybrid
It is first to a
parent.
AND
HYBRID
DESCRIPTION ANALYSIS
While
of pteridophytes Caledonia County,
collecting a series in
Vermont, montane 540 m)
discovered,
in a east-facing
I (ca.
pasture, an unusual clone o^Diphasiastrum which was not readily
referable to any described taxon. was growing with D. digitatum
It
and D. iristachyum but was clearly neither. Collections were made
August and November, from same
in 1993, the clone.
This plant has the general aspect of D. xsabinifoliuni with a
congested, tufted habit rather than pseudo-monopodial habit
a
such as characterizes D. digitatum and D. tristrachyum (Figure
This due to the branching of upright stems near their bases
is
1).
and to the length of the lower branches which reach beyond the
The
bases of upper branches. plant also similar to D. xsabi-
is
nifolium in short, usually unbranched peduncle with one or
its
A
two sporophylls on the peduncle below the strobilus. hybrid
however, was
origin, suspected because the lateral branchlets are
strongly dorsiventrally flattened, the lateral leaves are appressed
and
rather than spreading, the lower (ventral) leaves are reduced,
do
characteristics that not occur in D. xsabinifolium. Fur-
all
New
Oilman—
Tri-Hybrid Lycopod 289
1994]
CM
1
Figure Diphasiastrum digitatum x sabinifoUum. The influence of xsa-
1. Z>.
binifoUum indicated by the low branching, the indeterminate growth of branches
is
as shown by annual constrictions, and the unbranched peduncle with sporophyUs
The
scattered at the base of the strobilus (see details). broad, flattened branches,
reduced lower leaves and broad sporophylls are evidence of D. digitatum par-
entage.
and
thermore, the plant overall larger stouter than typical D.
is
x
sabinifoUum,
A
morphological analysis was undertaken to determine the
With
identity of this puzzling plant. such tests of hybridity as
DNA
garden experiments, isozyme or analysis lacking present,
at
Rhodora
290
96
[Vol.
Tabic Hybrid index comparing ten qualitative characters of the putative
2,
^
hybrid D. digilalum x sahinifoUuni and its parents. (2 character as in D. xsa-
= =
intermediate; character as in D. digitatum).
binifoliii}u\
1
Character (from Wilce, 1965) sab dig x sab dig
Habit congested due branching low
to
1.
on pseudomonopo-
upright stem,
vs.
dial 2
1
more
Branches indeterminate for 2 or
2.
shown
years, as by annual constrictions 2 2
Branches slightly glaucous, vs. bright
3.
green 2
1
4. Branches not or only slightly flattened
dorsiventrally 2
Lower leaves not reduced, vs. reduced 2
5. 1
6. Lateral leaves spreading vs. appressed 2
with narrow
Lateral leaves base, vs.
7.
broad
base
2
Fertile branch round with equal leaves
8.
(vs. flattened with reduced lower leaves) 2 2
Peduncle usually unbranched nor-
9. (vs.
mally branched) 2 2
Sporophyll narrow broad) 2
10. (vs.
Total 20 9
therefore, morphological comparisons give the strongest evidence
of hybrid
this plant's status.
A
series of hybrid indices (modified from Wilce, op. ciL, pp.
112-114) were prepared to compare this plant with potential
From
parents. these, was determined that D. digitatum and D.
it
most
xsabinifolium are the likely parents. Table 2 the index
is
prepared on often by which
the basis qualitative characters these
Of
probable parents the four character
differ. ten, states (irregular,
tufted habit; indeterminate branchlet growth; rounded
fertile
branch with isomorphic leaves; and unbranched peduncle) are
D
closest to xsabinifolium. Six characters (green coloration; dor-
siventrally flattened and appressed lateral leaves; broad bases of
reduced lower broad
lateral leaves, leaves, sporophylls) are closer
The
to D. digitatum. putative hybrid has an index score of
9,
intermediate between the scores of D. digitatum and D. xsa-
(0)
ifoli
Q
every
approaches one
parent or the other, or exceeds the parents
in
New
Gilman— Lycopod 291
Tri-Hybrid
1994]
Table Comparison of mean quantitative morphological characters, each
3.
Gilman Whee-
93241,
based on 30 measurements of dried plants {D. digilatum,
VT
Gilman Walden, and Gilman
VT; x 93246,
D. digilatum sabinifolium.
lock,
mm.
Marathon, measurements Standard deviations in pa-
92069, Ont.)- All in
rentheses.
Character sab dig X sab dig
Branch width 1.42(0.25) 2.01 (0.68) 2.52(0.57)
1.
Lower leaf width (base of free
2.
portion) 0.71 (0.09) 0.84(0.12) 0.53(0.12)
Low'-erleaflength (free portion) 2.28 (0.28) 1.32(0.15) 1.05(0.14)
3.
0.505
Ratio of lower leaf width/length 0.311 0.636
4.
48.5
Peduncle length 24.6 (7.2) 28.8 (6.24) (7.6)
5.
22.0
Strobilus length 21.6 (4.24) 30.6 (4.78) (1.40)
6.
Sporophyll width 2.28 (0,28) 2.02(0.14) 1.88 (0.17)
7.
Sporophyll length 2.08 (0.08) 1.98(0.10) 1.84 (0.09)
8.
Ratio of sporophyll width/
9.
1,09 1.02 1.02
length
mm
between
few Branchlel width 2.01 intermediate
a cases. at is
The
the parents. free portions of the lower leaves are intermediate
The
somewhat
in length, but are wider than either parent. pe-
duncle length intermediate, but closer to D.
ifoliu
is
Strobilus length greater than either parent, indeed greater than
is
(W may
be an
1965); this
may
anomaly of the individual plant or be the result of hybrid
The width and but
sporophyll intermediate length,
vigor. in
is
approaches D. digitatum in ratio of width to length (the ''com-
planatum type" of Wilce).
DISCUSSION
of hybrid
Accepting the hypothesis that D, sabinifolium
is
y^
genomes,
then hybrid has three ancestral D. digitatum,
origin, this
D. and D. tristachyum, presumably present in the pro-
sitchense,
portion
2:1:1.
some
Deviations from expected intermediate character states
may x
from
be inherited individually variable parents. sabi-
Z).
and
(Cody and
quite variable Britton, 1989)
nifolium
itself
is
may
variations in certain characters have been passed on to the
may
be due unequal contri-
hybrid. Alternatively, variations to
and
butions of the ancestral genomes, D, digitatum, D. sitchense
D. tristachyum. In particular, D. sitchense seems to be strongly
292 Rhodora
96
[Vol.
represented in the short unbranched peduncle (as opposed to the
and
long regularly forked peduncles of/), digitatum and D. thsta-
and
chyuin), in the low-branched, tufted habit (as opposed to the
pseudomonopodial
habit of D. digitatum and
D. tristachyum).
Another
potential hybrid combination, between
D. silchense
and D. xhahercri would have same genomes
the
in different
On
proportion
analogy with D. such
(1:2:1). xsabinifolitim, a
hybrid should display D. sitchense characters even more
strongly,
would be expected have
to non-flattened branches, spread-
i.e.,
it
ing lateral leaves, and unreduced lower leaves. Furthermore,
this
known
alternative unlikely because neither parent
is in the
is
immediate vicinity, whereas D. digitatum abundant the area
in
is
and known
D. sabinifoUum occur nearby
to (D.S. Barrington,
>< is
comm.).
pers.
As
noted above, species and hybrids Diphasiastrum mor-
in are
phologically distinct, and the hybrids arc apparently The
fertile.
barriers that prevent the hybrids from back-crossing and rehy-
swamping
bridizing to the point of the parent which
species,
maintain their distinctions over broad ranges, have not been iden-
The
tified. discovery of the hybrid discussed here
significant
is
because
suggests at least the possibility of introgression and the
it
On
formation
of hybrid swarms.
the other hand, both
dis-
its
and
tinctiveness confirm
rarity the current concepts of
its species
within the group.
Although may
spores are well-formed and be
its viable, this
known
hybrid as yet only from one There no
is site. direct
is
evidence that reproductively competent beyond surviving
is
it
and
slowly spreading For have
as a single clone. reason
this
I
chosen not provide an
to epithet.
MATERIAL EXAMINED
Wheelock
Mo
August and November
27 1993
(vt, nebc, mich).
1
ACKNOWLEDGMENTS
The
author thanks Warren H. Wagner and David
Bar-
Jr. S.
rington for discussions concerning the nature of and
this plant,
Martha Brown
S. for preparation of Figure also two anonymous
1;
reviewers comments.
for
New
Gilman— Lycopod 293
Tri-Hybrid
1994]
LITERATURE CITED
Beitel, M. 1979. The clubmosses Lycopodium sitchense and L. sabinifolium
J.
in the upper Great Lakes region. Michigan Bot. 18: 3-13.
Cody, W. D. and D. M. Britton. 1989. Ferns and Fern Allies of Canada.
Agriculture Canada, Ottawa.
Wagner, problems Lycopodium Ann. Mis-
F, 1992. Cytological in sens. lat.
S.
718-729.
Card.
souri Bot. 79:
Wagner, W, H. and M. Beetel. 1993. Lycopodiaceae, 18--37. In: Flora
pp.
J.
New
of North America, Vol. Oxford University Press, York.
2.
Nova
Hed-
WiLCE, H. 1965. Section Complanata of the genus Lycopodium.
J.
Wcinheim.
wigia Beih. 19.
BOX
P.O. 82
VERMONT
MARSHFIELD,
05658
