Table Of ContentTHE BRACTEOLES AMARANTUUS (AMARANTH
ACE
IN
AE):
THEIR MORPHOLOGY, AND
STRUCTURE, FUNCTION,
TAXONOMIC
SIGNIFICANCE
MihaiCostea^
Francois Tardif
J.
Department
of Plant Agnculture Department of Plant Agriculture
motphology and anatom>
of bractci
I
ci b> the presence oi \\d\ dt\ eloped
si
(choniKThdlJLo:
RESUMEN
noifologia anatomia de
y
1
INTRODUCTION
The genus Amaranthus group extremely high economical Some
a of value.
is
grown and
species are as vegetables pseudocereals (reviewed by Brenner
et
al.
among
2000), while others are the most important weeds of the world (Holm
et
some widespread ornamentals and they have
Additionally, species are
1997).
al.
and
a potential as forage crops as a source of red food colorants (Cai et al. 1988).
The taxonomical treatment of some species has proven to be problematic
(e.g.
&
Costea 2001; Xu Sun 2001), and proposed that characters of
et al. it is
may
bracteoles bring forward additional data useful for the classification of the
species within this genus. Bracts are modified leaves without an axillary bud,
(McCusker
associated with the inflorescence or with individual flowers 1999).
monocotyledons)
Bracteoles are secondary bracts borne singly (usually in or
(McCusker
in pairs on the pedicel, the calyx or the perianth of a flower 1999). In
The
Amaranthus, bracteoles should not be mistaken with the tepals. later are
which and
the units of perianth, not differentiated in a calyx a corolla
is
(McCusker As Brenan and shape longer bracteoles
1999). (1961) wrote: "the size of
in the inflorescence, and particularly their length relative to the flowers they
genus
subtend, are of great importance in distinguishing several species of the
morphology
Amaranthusr In the difficult A. hyhridus aggregate, the of
amaranths (Amaranthus
bracteoles has been used to differentiate grain
caudatus, A. cruentus and A. hypochondriacus) from their wild relatives (A.
and
hyhridus subsp. quitensis, A. hyhridus subsp. hyhridus A. powellii subsp.
(reviewed by Costea 2001). The length of bracteoles has also tra-
powellii) et
al.
some such
ditionally been used to classify the infraspecific variability of species
We
Thellung have proposed reevaluate the
as A. retroflexus 1914). to
(e.g.,
Amaranthus determine taxonomic
bracteoles in in order to their significance.
A
Kranz
mara nth us spp. are C4 plants and, therefore, exhibit the characteristic
&
anatomy in the leaves (best described in A. retrojlexus by Fischer Evert 1982)
and cotyledons (Wang No anatomical study of bracteoles has been
et 1993).
al.
m
published Anuiranthus, and would be interesting to compare their anatomy
it
may
with that of the leaves. Furthermore, the structure indicate their function
new
and could provide relevant data regarding the evolution of the genus.
Amaranthus spinosus the only species of the genus that exhibits two
is
two
spines the base of each and Thellung (1914) suggested that the spines
at leaf,
was
metamorphosed hypothesis another
are actually bracteoles. Testing this
objective of this study.
Morphology of female bracteoles was examined both on herbarium and fresh
material. Only the bracteoles subtending the flowers during fructification were
The were surveyed
taken into consideration. following herbaria collections for
BH, BRIT CAS, CLA, CM,
the nine qualitative characteristics (see below): BP, BPl,
DAO, DUKE, HAM, MICH, MIN, MO,
DAV, DS, FLAS, IBE, ISC, LA, LIL, MIL,
I,
MT UMO,
MSC, NA, OAC, OKL, PRH, QFA, RB, RSA, SMU, SOM, TEX, UCR, US,
VF
UTER VAB, VDB, and WIS. Additionally, bracteoles were collected from the
wild (mainly from Romania and Spain) and from cultivated accessions
flora
USDA
provided by the and Gatersleben germ plasm collections (Table Voucher
1).
BUAG USDA
specimens are preserved in the herbarium collection, except for the
which US
accessions, are preserved in the collection. For the anatomical study,
twenty were from each and 15-20
bracteoles collected plant, different plants
for each species were examined. Bracteoles were fixed in formalin-acetic acid-
alcohol (5:5:90) (FAA) and embedded in paraffin. Transverse sections were made
mm m
at 5-7 thickness and stained with Tolmdine Blue. The structure of the
bracteoles varies along with their length. The most complete region usually
is
mm)
and Draw-
at the base (0.2-0.4 of bracteoles, characters refer to this region.
ings were prepared with a Reichart camera lucida.
examined
List ofhracteoh characters (See the results section for additional ex-
planations.):
mesophyll more
iniform,
uniform, mesophyll
ot
is
Bundle
sheath:
..
050 Romania
(a-j)
Germany*
(k-s)
Nepal
16604
India
1
490440
Peru
subsp,qu/rens/5{Thell,)
Germany*
Romania
Dumort.)
Blitopsis
1
Germany*
Germany*
(Lesp.&Thev.
;pus
com, compact, enclosing the vascular
all tissu
frag, fragmented, separately acc(ompanyinge:
wmgs
Base of the containing:
.
m+s, with mesophyll +
sclerencl
m, only with mesophyll;
neither mesophyll nor ;hyma
sclerenc pres
-, is
luantitative characters of bracteol
.Length (mm);
Length spmose
of the apex-onl;yforspinosel
.
n bundle
collateral
ii
Tiesophyll (^m);
Dundle sheath
cells (^im);
length/ perianth
les length.
In all the species examined, each flower subtended by two bracteoles (some-
is
times only up which more
one, or to four) are or less modified compared to the
m
The Amaranthus
leaves. bracteoles can be
classified as follows;
a) Spinose bracteoles (Fig. A-F; Fig. 3A).-Are rigid and have a spiny
tip.
1,
They median
have
a part that includes the mid-vein surrounded by
scleren-
chyma
and mesophyll, and two membranous we name
lateral parts that shall
"wings," due to of their membranous appearance. The sclerenchyma more
is
developed than the mesophyll, conferring the hard and appearance
rigid of
As median
bracteoles. seen in cross-sections, the part can be semicircular
(Fig.
IC, E) semi-elliptic (Fig. ID), deltoid (Fig. IB, F) or even trilobed (Fig. 2A) (Table
The wings are not arranged in the same plane with the median They
2). part.
form a characteristic angle with the median part, which maintained even
in
is
Amaranthus
cross-sections (Table Representative
species: powellii
3). (Fig. IE).
2C-F) -Resemble more small and they
h)}oUauou\h>aitioLs{.¥\g a leaf
do not exhibit in obMOUi>diffei entiation between the median and lateral partb
and
mLsoph\ll more developed than the bclerenchyma as a result the
Hl
is
I
A
wmgs
icteoks mostly gieen The are narrow Repiesentative species
bi L
11
bhtouhsih^gll-V)
2B)-Rcsembk
OMimbninoushnideoksiFig
the lolitctous biacteoles
mid and
but the mesophyll pooil) developed lestiittcd ilon^ the \eins is
is
SekicnehMn ns
of ten reduced to the one layeied bundle sheath iKo scarcely
m
wmgs
thm mtmbi
developed The of the bracteole and inous (is the
lest is
A
thespmosebiacteoles) Repiesentatne species ui^pus Tiansitionalfoims
oi
between fohaceous and the membianous types occur in several species (A
the
A
Witumsubsp bhtum and
\uidis)
and
The structure of bracteoles simple: they have a dorsiventral structure,
is
they are composed of epidermis, mesophyll, vascular tissue and sclerenchyma.
monolayers
The marginal-meristem activity intense; its cells proliferate as
is
po/erafei;5,E-F./l blitoides.l.s
FiG.3. Structure of spir
±20
320 300 ±
+
±15
25 ±0.25 1.02 ±0.27 105 270 ± 30 220
±5
+
±0.5 7 ±0.1 7 135 230.5 30.5 203 i
1.3 2.1
±5 ±20 ±
240
165 162.5
±6
+
56 32
2
0.8-0.95
2.4
:
