TRICHOME MORPHOLOGY IN SELECTED MEXICAN RED OAK SPECIES (QUERCUS SECTION LOBATAE)

2006·13.7 MB·English

by  M Lucía Vázquez

TRICHOME MORPHOLOGY
SELECTED MEXICAN
IN
RED OAK
(QUERCUS SECTION WBATAE)
SPECIES
M. Vazquez
Lucia 1
Department of Plant Biology
Cornell University
New
USA.
Ithaco, York 14850,
[email protected]
ABSTRACT
Mature leaves and twigs from thirty red oak species, mostly endemic to Mexico, were examined with SEM
to
assess tnchome morphology Ten trichome types were identified; two glandular and eight nonglandular Described
for the first time in the oak literature are fasciculate contorted, fasciculate crested, and multiple stellate trichomes.
Furthermore, three trichome types are reported for the first time in red oaks: stellate, fused stellate, and glandular
common
branched. The most types on the twigs examined are fasciculate sessile and multiradiate trichome while
the most frequent types on the abaxial leaf surfaces are fasciculate sessile, fasciculate stipitate, and multiradiate
m
trichomes. In contrast to the significant morphological variation found oak leaf shape, trichome complements
within each and
species are nearly invariable therefore useful in the identification of most species. In summary,
together with vegetative and reproductive characters, trichome morphology provides additional information
for
the identification and characterization Mexican oak
of species.
RESUMEN
Hojas maduras
y ramillas de creinta especies de encinos rojos, princtpalmente endemicos a Mexico, fueron
exammadas
con microscopia electronica de barrido para evaluar variacion morfologica de tricomas. En
la este
trabajo sc identificaron diez tipos de tricomas; dos glandulares y ocho no glandulares. De estos, se dcscriben por
primera
vez para encinos los tricomas fasciculado contorto, fasciculado crestado y estrellado multiple. Ademas,
se reportan por primera vez para encinos rojos tres tipos de trichomes: estrellado, estrellado fusionado glandu-
y
lar ramificado. Los tipos de trichoma mas comunes en ramillas son fasciculado multiradiado, mientras
el sesil y el
que en el envcs de las hojas los tipos de tricoma mas frecuentes son fasciculado sesil fasciculado estipitado
el y el
m
Aunque
multiradiado. los encinos uestran una gran variacion en moriologia los tipos de tricomas presentes
foliar,
muy
en cada especie son constantes por lo tanto son utiles en la identificacion de la mayoria de las especies. En
y
resumen,
los caracteres vegetarivos reproductivos junto con morfologia de trichomes proporcionan
y la
informacion valiosa para la identificacion y caracterizacion de las especies Mexicanas de encino.
INTRODUCTION
Q
distributed in temperate and subtropical regions of the Northern Hemisphere. In the
Q
Quercus: Q
mediate oaks), and Lobatac (red oaks) (Nixon 1993). Due to the large diversity of white
m
and Mexico New
red oaks, is considered the center of diversity for the genus the World
(Rzedowski Nixon
1965; 1993).
The number
of red oak species has been estimated around 195 (Jensen 1997) with
about 55 species endemic to Mexico (Nixon 1993). In his treatment on the American oaks,
Trelease (1924) segregated the red oak species into 73 series and also proposed a classifi-
cation based on leaf and fruit morphology. However, his hypothesis on the relationships
of red oak species has not been with phylogenetic methods. Although mono-
tested the
Current address: Biology Department, University of Illinois Springfield at Springfield, Illinois, 62794, U.S.A
mo.
SIDA 1091- 2006
22(2):
1092 BR1T.ORG/SIDA 22(2)
Manos
phyly of the red oak section well supported (Nixon 1984; 1999), an intrasectional
is
phylogeny for the red oaks is yet to be conducted. As in otlier oak groups, Mexican oak
them show amounts
species are difficult to study because most of significant of lobar
when
polymorphism. becomes even more complex hybridization
Species identity either
many
taxonomic problems oak
or introgrcssion has taken place. Therefore, in species
particularly in those species that have similar or overlapping leaf morphology.
persist,
The trichome morphology species identification has been demonstrated
utility of for
and (Inamdar
in several plant families such as Brassicaceae, Gcraniaeeae, Sterculiaccac
& &
Shanmuka Rao
Rao Chalk Oosthuizen
1983; Metcalfe 1950; 1983; 1987). In oaks, tri-
chome characterization has been carried out several eastern North American, Asian,
for
and FAU'opcan species. The first study on trichome morphology of eastern North Ameri-
who
can oak species was reported by Dyal in 1936, classified them, based on secretory
Camus
glandular and nonglandulan (1934-1953) described seven trichome
function, into
types that into the glandular and nonglandular categories previously described by
fall
Dyal Hardin published comprehensive work on oak trichome mor-
(1936). (1976) the first
phology for 58 eastern United States (US) oak species and recognized 10 trichome types.
Thomson and Mohlenbrock and Manos conducted
Jones (1993b) similar
(1979), (1986),
on oak Trichome morphology European and Mediterranean
studies otlier U.S. species. oi
documented
oak species has also been extensively by several authors (Olsson 1976;
&
Kisslmg 1977, 1993; Safou Saint-Martm 1989; Cellini et al 1992, Llamas et al. 1995;
&
Grossoni Trichome morphology, together w^th other vegetative and
Bussotti 1997). re-
productive characters, has been used to discriminate several U.S. oak species, as well as a
&
few Mexican species distributed in the northw^est of the country (Tucker 1952; Tucker
& & &
MuUer
Nixon Nixon Bacon
Mullcr Spellenberg
1957; Steele 1981; 1992, 1998; 1993;
Spcllenberg However, no in-depth research on the trichome morphology
1996). to date,
of Mexican taxa has been carried out. Several regional taxonomic treatments of Mexican
oak species have been conducted (Gonzalez 1986; Valencia 1989, Vazquez 1992, 2000;
Spcllenberg Spellenberg but none them has characterized trichome
1998; 2001), of
et
al.
diversity. Only a few authors have discussed the potential utility ol trichome types for
&
Mexican (McVaugh Vazquez
ielentification of species 1974; Rzedow^ski Rzedow^ski 1979;
trichome morphol-
1992). Accordingly, the objective of this study to characterize the
is
ogy from twigs and leaves from thirty Mexican red oaks, mainly endemic to Mexico, us-
ing scanning electron microscopy (SEM). Detailed examination these species revealed
ol
the presence of ten trichome types: four of these trichomes have been previously described,
new
three of them represent entirely trichome types, and the remaining three are
tri-
chome documented Each examined shows
types not previously for red oaks. species a
particular trichome complement which, together with other vegetative and reproductive
and
characters, provides useful iniormation for species identification characterization.
METHODS
MATRRIALS
AiND
Leaves and twigs from thirty species of red oak species chiefly endemic to Mexico were
examination trichome morphology under SEM. Nixon has reported
selected of (1993)
for
indument
41 red oak species endemic to Mexico, of which, twenty-one have persistent
and were sampled Two with indument
in this study. additional species persistent
(Q.
castanea and Q crassijolia) w4iosc range extends to Central America wTre included in
this study because they are widely distributed in Mexico. For comparison, six glabrous
1
VAZQUEZ, TRICHOME MORPHOLOGY QUERCUS 1093
IN
Table Red oak species (Quercus) examined with SEM for trichome morphological variation. Voucher speci
1.
mens
are deposited at Bailey Hortorium, Cornell University (BH).
Taxa Voucher specimen
Q. acherdophyllo Trelease Vazquez etal. 3065
Scheidweiler Muller 97
Q.affinis 16
Hooker & Arnott Martinez Breedlove 1640
0. aristota 31,
condicons Nee Vazquez 3095
Q. etal.
Q.castanea Nee Rzedowski 25361
coahuilensis Nixon & Muller Stewart 924
0.
Vazquez & 3084
Q. coccolobifolio Trelease Phillips
GconzaftiVTrelease Muller 9420
Humboldt & Bonpland Vazquez 3049
Q.crassifolia etal.
Humboldt & Bonpland Vazquez 3070
Q.crassipes etal. 3037,
Humboldt & Bonpland Vazquez &
Q.depressa Tenorlo 18
1
von Seemen 3579
Muller
Q. durifolia
Bentham
0.x dysophylla Nixon (Oct. 1999)
s.n.
Q. eduardii Jrelease Nixon 4034, Vazquez et al. 30
1
Liebmann Vazquez 3097
0-fulva etal.
McVaugh
25635
Q.gentryi Muller
Warburg Vazquez 3029
Q./i/nfon/7 etal.
Q.hlntoniorum Nixon & Muller Eckelman 2 1 Poole 2336
Vazquez, Valencia & Nixon Vazquez etai 3069, 3 109
Q./7/rf/fo//a
Camus & 8338
Q.hypoleucoides Yen Estrada
Cowan
hypoxanthoJrelease 5402
Q. etal.
mcvaughil Spellenberg Bocon 5284
Q. etal.
mexicana Humboldt & Bonplanc Rzedowski 6374
0,
McVaughl2136
0.p/an/pocu/{7 Trelease
Rzedowski 23018
radiata J[e\ease
Q.
Nee McVaugh 25456
Q. sal folio
ici
Liebmann Vazquez 3035
Q.scytophylla
et
al.
Humboldt Bonpland Vazquez Bacon 5304
Q. sideroxyla 8^ et al. 3089, et al.
larahumQro Spellenberg, Bacon & Breedlove Bacon 5307, 5375
Q. etal.
Vazquez 3027
c/rdan/7Trelease etal.
Q.
red oak species endemic Mexico were included. Samples of the materialexamined were
to
gathered from field collections and from herbarium specmiens deposited at the Bailey
Hortorium, Cornell University (BH) (Table
1).
Twenty thirty specimens per species were initially examined under dissecting and
to
m
and tnchome morphol-
light microscopy to survey the intra- interspecific variation
SEM
ogy A more detailed examination was carried out under in representative
cm cm
subsamples. About one square of the abaxial surface of a dry leaf or one of twig
shown
was mounted on an aluminum stub with no prior treatment. Previous studies have
tnchome
no difference in the preservation of nonglandular structure using either fresh
dry (Hardin Specimens mounted on stubs were sputter coated with 30
or tissue 1976).
nm
BAL-TEC
of gold palladium using a sputter coater. Samples were observed under a
DSM
LEO
microscope, model using working distances between 12 and
Zeiss electron 960,
mm,
18 voltages of 3.0 or 4.0 kV, and apertures of 300 j.im or 400 jam depending on the
sample and magnification. Most trichome micrographs were taken magnifications of
at
450-500x.
200x, although smaller trichomes required magnifications of
i
1094 BRIT.ORG/SIDA
22(2)
Taiu 2,Trichome types on twigs of Mexican red oak species {Quercus)
I
Species Glandular Nonglandular
Simple Branched Fasciculate Fasciculate Multiradiate Simple
uniseriate sessile simple stipitate Stellate
acherdophylla X
0.
X
0- affinis
Q.aristato X
candicans X X X
0.
Q.castonea X
Q.coabuilensis X X
coccolobifolia X X
Q.
conzattii X X
Q.
Q.crossifolia X X X
Q.crassipes X X
depressa X
Q.
duri X X
0, folia
X
dysophylla X X
Q.
eduardli X X
Q.
0, fulva X X
gen X
Q. try!
Q.hintonil X X
Q.hintoniorum X X
X
Q. hirtifolia
hypoleucoides X
Q.
hypoxantha X
Q.
mcvaughii X X
Q.
mexicana X X
Q.
Q.planipocula X
fad
Q. iota
X
Q. salicifolia
scylophylla X X
Q.
X
Q.tarahumara
urbonii X X
Q.
RP.SULTS
Trichomc nomenclature follows Hardin where each composing nonglandular
(1976), cell a
named
trichome is called a "ray" and tricliomc types are based on the degree of ray fu-
and morphology
sion, ray orientation, overall However, additional terms have been
in-
troduced to describe trichome types not previously reported in the literature.
Two
general trichome categories are used to indicate secretory functions and nature
of the cell wall: glandular trichomes have a glistening appearance and thin walls
1) cell
upon
that collapse drying, and 2) nonglandular trichomes lack a glistening appearance
and possess thick cell walls. Examination of twigs and abaxial leaf surfaces of thirty red
oak species resulted in two types of glandular trichomes and eight nonglandular trichomc
and
types (Tables 2
3).
Glandular trichomes
IB)—
Simple 2-7
1. uniseriate (Fig. lA, This type consists of united cells with slight
constrictions along the trichome length. This trichomc type was commonly found on
indumentum
Table S.Trichome types in oak species {Quercus) with a persistent on tlie abaxial leaf surfaces
t^
Species Glandular Nonglandular
r-j
Simple Branched Fasciculate Fasciculate Fasciculate Fasciculate Multi- Simple Fused Multiple r^
uniseriate sessile sessile sessile stlpitate radiate stellate stellate stellate
simple contorted crested
Q.acherdophyHa Xv
of Xv
Q. fin
is
n
X
oristota
Q.
Q.candicans X X X X
Q.castanea X X
uo
Q.coahuilensis X X
X Xv
coccolobifolio
Q.
Q.conzattii X
X
X X
Q. crassifolia
X
crossipes X
Q.
depressa
Q.
Q. durifolla X X
X X
dysophylla X
Q.
Q.eduardii X
X X
Q. fulvo
gentry! X X
Q. Xs
Q. hinton a X X X
Q.hintoniorum X Xv X
X
X
Q.hirtifofiQ
X
Iiypoleucoldes
Q.
Q.hypoxantha X X
Q.mcvaughii X X
Q.mexicana X X
Q.planipocula X X
Q. rod ata X X
I
Q.solicifolia Xs
s
X
scytophyllo
Q.
sideroxyla X X X
Q.
torabumora X X
X
Q.
X
Q. urbanii X
s=scatterec v^trlchomes on seconaary veins
1096 BRIT.ORG/SIDA
22(2)
LA,
Fig. Thin cell wall in a glandular trichome of (?i/era/5coffo/o&/yo//f7. X40.B. Glandular simple uniseriatetrichome on the abaxial
leaf surface o^Q.hintoniorum,X500. C, Glandular branched trichome on the abaxial surface oi Q. salicifofia, X500. D. A variation of
X
the glandular branched trichome on the abaxial leaf surface of Q. salicifolia, 500.
the abaxial leaf surfaces of twenty-one species, forming sparse and deciduous
a
indumentum. In most species examined, density decreased during matu-
trichon^ie leaf
and Que showed
ration senescence; however, reus coccolohijolia persistent simple uniseriate
trichomeson the abaxial leaf surface. This trichome type was found on the twigs of only
achcrdophyUa, and
three species: Q. Q. coccolohijolia, Q, crassiJoJia (Table 2).
V
2. Branched (Fig. JC, ID).— This type consists of 2-3 cells united in either a or a Y
shape; however, under the dissecting microscope this trichome type looks like two uni-
cellular simple trichomcs lying next to each other This trichome type was found exclu-
on
sively abaxial surfaces
oi Q. salicijolia leaves.
Nonglandular trichomes
Fasciculale sessile irichomes— These consist of several rays fused at the point of attach-
ment to the epidermis. The rays are either short and completely erect (Fig. 2A), or long
VAZQUEZJRICHOME MORPHOLOGY QUERCUS 1097
IN
X200.
Fig. 2. A. Fasciculate sessile simple trichome on the abaxial leaf surface of Quercus aristata, B. Fasciculate sessile simple tri-
chome on the abaxial leaf surface of Q. crassifolia, X200.C. Fasciculate sessile contorted trichome on the abaxial leaf surface of Q.
X
mexicana, X200. D. Fasciculate sessile contorted trichome on the abaxial leaf surface of Q. eduardii 200.
and tortuous diverging in different directions (Fig. 2B). Three types of fasciculate sessile
trichomes are recognized in the species examined.
Fasciculate sessile simple (Fig. 2A, 2B).— The fasciculate sessile trichome described
1
.
Hardm
by (1976; 1979a) and Jones (1986) termed here fasciculate sessile simple to dis-
is
was
tinguish from the two additional subtypes listed below. This trichome type tound
it
on
on twigs and/or on the abaxial leaf surfaces of several species examined. occurs
It
twigs of the following species: Q. candicans, Q. castanca, Q. coahuilensis, Q. coccolohifolia,
9 z Q.crassifolia,Q crassipes, Q. du rijolia, Q. x dysophylla, Q. eduardii, Q.fu Iva, Q.
hintoniorum, hypoleucoides, hypoxantha, mcvaughii,
Q. Q. hirtifolia, Q. Q. Q. Q.
tarahumara and
planipocula, radiata, scytophylla, sideroxyJa,
Q. Q. Q. Q. Q. Q.
2,
on
Species bearing this trichome type abaxial leaf surfaces are aristata,
Q. Q.
hypoxantha,
Q. coahuilensis, Q. crassijolia, Q. hintonii, Q. hirtifolia, Q. Q.
,
and tarahumara
radiata, (Table
a, Q. Q. 2).
1098
BRIIORG/SIDA
22(2)
2C 2Dj—
2. FasciciiJatc sessile contorted (Figs. This study describes this trichome
type for the first time. Contorted trichomes arc similar to the fasciculate sessile simple
down
trichome described above except that the rays curl and then twist around the
tri-
chome
This arrangement indumentum when
axis. ray gives the punctate appearance
a
observed with naked
the eye or at low^ magnification. This trichome type has been found
on andO
the abaxial mexicana
Q.
cduanlii.
new
3. Fasciciihitc sessile crested (Fig. 3A).— This is a trichome type that consists of
rays united along a longitudinal axis oriented parallel to the epidermis. The united rays
result in a structure that resembles a crest. Trichomes of this type were found only on the
some
abaxial surface of sideroxyla specimens.
Q.
30.—
4. Fascicu late stipitate (Figs. 311 Morphologically, this trichome type similar
is
to the fasciculate sessile simple except that the basal parts of the rays fuse, forming a
The among
stipe. degree of ray fusion varies species from 1/12 to 1/4 the total ray length.
Ray and
length degree of divergence are also different; some species display short and
show
straight rays (Fig. 3B) while others long curly rays that become intertwined with
adjacent rays (Pig. 3C). Ray number variable within and among although m-
is species,
traspecific ranges are low. Fasciculate trichomes form indumentum
stipitate a persistent
on
the abaxial leaf surface of the following
species: conzattii,
Q. Q. crassifolia, Q. crassipes,
Q.xdysophyUa,Q.hintonii,QJ}iriiJoUa,Q.pJanipocula,QAara}uimara/3in^
Q
acherdophyUa,
Q
Q. Q. affinis,
Q
de
ijolia, Q. pre ssa, •and
s
remain
attached to the epidermis at the secondary vein Fasciculate
axils. stipitate
tri-
chomes on common
twigs were and found only
less in aristata, coahuilensis,
Q. Q. Q.
and
x dysophylla
crassifolia,
Q. Q. h
rt iJoJia.
i
Mull 4A
radiate 3D, 4Bj.— This trichome
5. (Figs. type characterized by the diver-
is
i
gence from
ot rays in different directions the central axis. In the species examined, the
rays differ not only in length but also in thickness. Multiradiate trichomes were found on
caudicans, durijolia, QJuJva, Q
Q. Q.
Q
th c Q. ajjinis, Q. conzaitii, Q. crassipes, Q. devressa, Q
Q.genlryiO
Multiradiate trichomes occurring on
abaxial leaf surfaces usually form persistent
a
if^
the lamina.
4Q
6. Simple stellate (Figs. iD, 5A) -This trichome type consists of rays appressed
to the lamina, usually fused forming
at their base, a structure that resembles a starfish.
Simple stellate trichomes are composed of seven to fifteen rays, which vary in length,
thickness, and size. This trichome type was previously described by Hardin and
(1976)
Jones (1986) under the term stellate. Here the term simple stellate used to set apart
is
it
from and
the multiple stellate fused stellate also found in this study Simple
stellate
tri-
chom
es the twigs of acherd
Q.
Q-durih
ca}}dicans,
Q.
5B)— new
Multiple stellate (Fig. This trichome type consists 2-3
7. of stellate
tri-
chomes
joined together forming a trichome cluster. was found only on one species, scat-
It
on
tered the abaxial leaf surface of Q-gentryi.
VAZQUEZJRICHOME MORPHOLOGY QUERCUS
IN 1099
X450.
Fig. 3. A. Fasciculate sessile crested trichome on the abaxial leaf surface of Quercus sideroxyla, B. Fasciculate stipitate trichome
on the abaxial leaf surface of Q. aristata, X200. C. Fasciculate stipitate trichome on the abaxial leaf surface of Q. conzatti X200. D.
Multiradiate trichome on the abaxial leaf surface of Q. salicifolia, X500.
5C)—
8. Fused stellate (Fig. This trichome type previously described by Hardin (1979a)
and
Jones (1986) consists of rays fused about one sixth of the ray length. This trichome
was
type, not previously reported for red oaks, found exclusively on the abaxial leaf sur-
face of candicans.
Q,
DISCUSSION
m
SEM
The
study trichomes with
of revealed significant differences trichomes that ap-
when
peared similar viewed with dissecting microscopy These differences have allowed
a more accurate characterization of trichome types and have also led to the discovery of
new
nonglandular trichome and
three types: fasciculate contorted, fasciculate crested,
multiple stellate. Fasciculate contorted trichomes, although recognized as a different type
by several authors (McVaugh 1974; Gonzalez 1986). had been included under the stellate
1100 BRIT.ORG/SIDA 22{2)
X300.B.
FiG.4.A.Multiradiatetrichomeontheabaxiaisurfaceof(?we/'(:i;5£/wnMa, Multiradiate trichome on the abaxial leaf surface
x
X
oiQ.scytophylla, 500. C. Simple stellate trichome on the adaxial leaf surface of Q. eduardii 500. D. Simple stellate trichomes on
X800.
the twigs oiQ.acherdophylla
new
The
second trichome simple found only on
type. type, fasciculate crested, the
is
uncommon
some The
abaxial leaf surface of Q. sidcwxyla specimens. distribution of fas-
ciculate crested trichomes suggests that they could represent variation of the
a
multiradiate type, which an abundant trichome type in the indumentum of
is Q.
m
The new
sidcwxyla. third trichome type, multiple stellate, found a scattered pattern
is
exclusively on the abaxial leaf surface of Q.gcJitryi. Under the dissecting microscope this
SEM
trichome resembles a multiradiate type but close examination with reveals that
it
consists of two to three stellate trichomes fused together (Fig. 5B). Therefore, trichomes
that appear multiradiate must be examined carefully to avoid inclusion of multiple stel-
late types into this category For example, Hardin (1979b) described a trichome type as a
dense multiradiate, however, his corresponding illustration (Fig. 30) shows a morpho-
logical resemblance to the multiple stellate type described here.
new new
In addition to the trichome types found in this study three types represent