The single section shown (fig. 103) will serve to indicate the nature of the
seed coat in this genus. The number of layers outside of the inner two may be
greater or fewer than that shown, but is never fewer than three cell layers and
usually more, depending on ring formation. The outermost layer of cells consists
of thin-walled sclereids. A number of thin-walled but persistent cells
are present between the epidermis and the inner pair of cell layers. The
persistent tissue is distinctive only in the presence of intercellular deposits,
which occur in irregular patches and are of the same material Avhich fills lumina
of the innermost pair of cell layers of the seed coat. The inner two cell layers
are distinctive, as in Abolboda, in their occlusion with the resin-like or tanninlike
contents. In origin and nature, these cell layers are precisely homologous
with those two layers in Abolboda. The outer of these layers does not exhibit
the remarkable alteration into ridges which occurs in Abolboda, however.
Comparison of Seed Coats in Xyridaceae.
Unfortunately, no seeds of Achlyphila distich a were available. There are
descriptions of seeds of Xyris in the literature, although only for one species,
X. indica (Weinzieher 1913; Netolitzky 1926). These descriptions show a layer
of cells with dark contents, formed into longitudinal ridges on the seeds, which
has sculpturing on the outer wall surface and appears to correspond with the
similar layers with contents in Abolboda and Orectanthe. Weinzieher, however,
suggests that the origin of this layer is from the inner layer of the outer integument,
rather than the outer layer of the inner integument, as is the case in
Abolboda. Careful comparative studies of ovules in Abolboda and Orectanthe showed that the outer thin-walled layers, without contents, are derived from the
outer integument, whereas the inner pair of cells with occluded lumina are
derived from the inner integument. From very casual observations on seeds of
Xyris, the writer is of the opinion that the respective layers in Xyris actually
have a similar origin, and that the interpretation of Weinzieher is open to
The differences in seed structure between Abolboda and Orectanthe appear
to be very distinctive expressions of the same basic pattern, and may be used
both to separate the genera and to emphasize an underlying similarity. The
writer believes that seeds of Xyris, upon further study, will probably also reveal
similar conspicuous variations on a pattern common to the whole family. Study
on seeds of Achlyphila is needed for the same reasons.
Weinzieher (1913) and Netolitzky (1926) indicate rounded compound
starch grains and protein spheroids in endosperm of Xyris. Presumably both
of these accounts are based on Weinzieher's study of X. indica. All the species
for which material was available of Abolboda (fig. 101) and Orcctanthe showed
these features. Immature stages in the endosperm of .1. sprueei showed the
multinucleate condition of endosperm cells very clearly.
Weinzieher (1913) has illustrated stages in the development of the embryo of
Xyris indica. The embryo consists of relatively few cells. A broad, flat cotyledon
is evident, but Weinzieher figures no differentiation of a suspensor or any meristematic
region. Features like these occur in Abolboda, as illustrated for
A. americana in figure 101. A basal and a hypoba^al cell are evident, however.
The cotyledon consists of large cells, with dark-staining contents that suggest the
haustorial function of this structure which is closely appressed to the endosperm.
At the edges of the cotyledon, flap-like extensions are evident. The embryo of
Abolboda americana shows no differentiation of an apical area, and is larger and
composed of more numerous cells than that of X. indica. Significantly, the
embryo of Orectanthe seeptrum (fig. 102) shows precisely the same features as
the embryo of Abolboda americana, but is larger, corresponding to the larger
size of all org-ans in this species. A basal and a hypobasal cell appear to be
present. If a meristematic area is present, it is not appreciably differentiated
from other areas of the embryo. Unfortunately, no embryos of Achlyphila were
available. Likewise, no stages in gametogenesis or early embryo development
were visible on account of the nature of preservation.
Pollen grains of Xyridaceae are subject to decomposition by various reagents. As Erdtman (1952) notes, his acetolysis method degrades the exine. Sodium hydroxide, a reagent commonly used in pollen-preparation techniques, partly or wholly dissolves the exine. Except for two specimens (figs. 112, 120) in which NaOH treatment was very gentle and merely revealed some textural differentiation
in the exine—probably because of preferential solubility of certain
parts—this substance proved useless. Even the pollen of fixed material which
formed the main basis for this study was, in some cases, altered. Because of
this extreme sensitivity to a wide variety of reagents, the simplest methods for
preparation of pollen grains for observation appeared to be (1) sectioning and
staining of flowers (with their included pollen) according to the techniques
described at the beginning of this paper; and (2) transferring fixed anthers
through an alcohol series to absolute ethyl alcohol, staining in safranin dissolved
in absolute ethyl alcohol, and following- this by transferring anthers to xylene
and making wThole mounts of grains in Canada balsam. Undoubtedly both of
these techniques resulted in dehydration and perhaps other changes which could
alter size and possibly induce artifacts. However, a number of grains in each
of the collections studied appeared to be reasonably unaffected, and were considered
suitable for study. Note should be made of the fact that the spines (or
other excrescences of the exine) that stain bright red are seemingly unchanged
by any of the reagents mentioned, and data concerning these are without doubt
quite reliable. The exine wall, which stains green with a safranin-fast green
combination, is the structure that is sensitive to reagents.
Because the grains are large, and few in number per anther, because good
material (grains from anthers just before or at anthesis) were necessarily
limited, and because many grains were collapsed, or degenerate, the number of
grains that could provide reliable measurements was extremely small. The data
on pollen grain diameter below represent, therefore, averages of measurements
of only those grains that the writer judged to be turgid and otherwise unaltered
in form. On account of the exceptional susceptibility of pollen grains in this
family to various changes, truly exact data can probably be obtained only from
fresh material. Such material is virtually impossible to view because of the
remote locations in which these species grow. Terminology for pollen morphology
used below follows the usage of Erdtman (1952).
Pollen Grain Size.
Pollen grains of Abolboda, Orectanthe, and Achlyphila are sphaeroidal, a
fact which may be related to their nonaperturate condition. Because of this
shape, only one dimension is necessary. Dimensions do not include the spines
or other excrescences.
Within the genus Abolboda, some taxa seem obviously to have larger pollen
grains than others; species with exceptionally large grains include A. linearifolia,
A. macrostachya (at least in part), A. grandis, and A. sprucei. The pollen grains
of Orectanthe are markedly larger, in general than those of Abolboda. The
markedly smaller diameter of Achlyphila pollen grains is interesting; this size is
comparable to the sizes reported by Erdtman (1952) for species of Xyris. Pollen
grains of Xyris, as described below, do differ in morphology from those of Achlyphila.
Previous reports on pollen-grain diameter include those of Malme (1933) on ''Abolboda" (now Orectanthe) sceptrum ("about 105 µ") and Erdtman (1952) for Abolboda poarchon ("105 µ"), A. pulchella ("105 µ"), and A. vaginata ("at least 75 µ"). Maguire, Wurdack et al. (1958) give the following measurements: Abolboda bella, 120-140 µ; A. paniculata, 140-150 µ; and Orectanthe (as a genus), 160-250 µ.
Pollen Grain Wall ("sporoderm").
Sectioned material showed two distinct parts of the pollen grain wall in all
taxa: the inner portion, which stains brightly with fast green, and the spines,
or other ornamentation (including the minute pila on the surface of the interspinal
areas), which stain bright red with safranin. These two portions appear
to correspond with Erdtman's definitions of nexine and sexine respectively,
except that a thin layer, which stained pale green, on the inner surface of the
pollen grain wall in Abolboda could be interpreted as the intine. This interpretation
was suggested by observation of germinating pollen grains on a style of
A. grandis. In these, this layer covered the emerging pollen tube. Such a layer
could not be distinguished in pollen grains of Orectanthe, possibly because of
difficulties in preservation, but a comparable layer did appear present in grains
of Achlyphila (fig. 128).
The nexine in sectioned material and in whole mounts appears to stain
homogenously in most preparations. In two preparations in which sodium
hydroxide had been employed (fig. 112, 120), radial fibrillae or striae appeared
to be present in the outer two-thirds of the nexine. This appearance may have
been caused by differential solution of materials in the nexine, or by expansion
of the wall by means of the treatment. Among the various taxa, the nexine
thickness appears to be a distinctive character. In most of the Abolboda species
studied, it appears to range between 5 and 7 p. It is much thicker than that in
A. grand/is var. guayanensis, A. macrostachya var. macrostachya, A. niacrot
achy a var. robustior, and A. sprucei. Certainly the great thickness of the nexine
of A. grandis var. guayanensis and A. sprucei represents a distinctive characteristic.
In Orectanthe, the nexine does not appear to exceed 5 fi in thickness. In
Achlyphila, the width of this layer is about 3 µ.
The outermost layer of the pollen grain wall, or sexine, is basically a thin membranous layer which may be partly detached in damaged grains. Minute
pila (seen in surface view, figs. 113, 129) are embedded in this membrane. A
feature that seems quite important to the writer does not seem to have been
mentioned in the literature on Xyridaccae pollen grains, namely, that these
minute pila are, in fact, homologous with the large spines or knob-like ornaments
in Abolboda and Orectanthe. These larger excrescences are deposited on the
membranous layer just as the pila are, and appear to be composed of the same
material, despite the vast difference in size between the two types of ornamentation
on the same grain. Rarely, as in Orectanthe sceptruin (fig. 125), knobs
transitional in size between these two categories may be observed. The pila in
Orectanthe are noticeably larger than those in Abolboda. Pollen grains of
Achlyphila (figs. 128, 129) show the largest pila of any of the grains studied
here. In Achlyphila, the pila tend to be aggregated in flake-like patches. In places between these patches, the pilate layer is absent. In Abolboda, a thin hyaline layer was observed immediately beneath the pilate layer. Such a layer may also occur in pollen grains of Orectanthe and Achlyphila.
The spines on pollen grains of Abolboda are so characteristic of that genus, and are so subject to distinctive variations in the species, that they have been figured for all the species studied (figs. 106-120). Basically, as in A. acaulis or A. linearifolia, they have an inverted funnelform shape. Sodium hydroxide treatment (figs. 112, 120) reveals that lacunae, not visible in other preparations,, are probably present in the spine base. Some species show markedly narrow spines: A. bella (fig. 108), A. acicularis (fig. 107), and A. ciliata (fig. 109). Very short, wide spines occur in A. ebracteata (fig. 110) and A. macrostachya var. robustior (fig. 120). The three varieties of A. macrostachya appear different on the basis of spine size and shape. Within a single flower of A. sprucei, various alterations in spine shape were noted. The basic condition seems to be that shown in figure 114, but multiple spines on a single base (fig. 115), very much reduced lobes (fig. 116), and merely the vestige of the spine-base (fig. 117) were also observed.
Erdtman (1952) has illustrated the spines of pollen grains of three species and given dimensions: A. poarchon (spines 8.3 µ long; basal diameter 5.5 µ), A. pulchella (spines 9.3 µ, long; basal diameter 8.3 µ), and A. vagineita (spines 8.3 µ long; basal diameter 8 µ). Erdtman figures spines in the latter species which appear about like the spines in A. macrostachya var. angustior.
The comparable ornamentation on pollen grains of Orectanthe is generically different from that of Abolboda. In Orectanthe, the emergences take the form of a large knob, or other shape much wider and more blunt than the spines of Abolboda, with the possible exception of the much smaller structures in A. sprucei. In O. ptaritepuiana (figs. 121-124) a variety of shapes was noted, varying with the collection from which the grain was taken: short, with a rounded apex (fig. 121), elongate (fig. 122), with a curved apex (fig. 123), or with folds or bulges on the sides (fig. 124). Evidently considerable variation is present in these characters. In preparation of pollen grains in this species, the knobs appeared to be sunken in slight depressions; this may well be an artifact of fixation or preparation. The knobs of Orectanthe seeptrum pollen grains are different from those of 0. ptaritepuiana in that the apical portion is widened, so that a capstan-like shape is achieved. The only variation in structure of these knobs is found in the formation of additional small knobs on the base (fig. 127) as compared to the normal condition (fig. 125), or the formation of a roughened base (fig. 126).
In summary, the pollen grains of the three genera show excellent generic
characters. The presence of large excrescences in Orectanthe relates this genus
closely to Abolboda, but the differing shape is a good generic character. Likewise,
the larger pila in the surface between emergences differentiates Orectanthe
from Abolboda. The absence of such large emergences in Achlyphila, and the
grouping of pila into flake-like aggregations on the exine surface, marks this
genus off from other genera of Xyridaceae. Within Abolboda, differing exine
widths and distinctive spine shapes and sizes serve to differentiate the species,
so that of the species studied, most could be identified by means of the pollen
grains alone. Similar considerations apply to distinctions between the two
species of Orectanthe.
Erdtman (1952) has emphasized the great distinction between Abolboda and
Xyris in pollen-grain structure. Much of this distinction may be attributed
to the large spines on the surface of Abolboda pollen grains. The lack of such
larger ornaments on grains of Achlyphila, which are (like those of Abolboda,
but unlike those of Xyris) nonaperturate, may vitiate this contrast, and provide
an intermediate form. The pilate layer in pollen grains of Abolboda, Orectanthe,
and Achlyphila probably has a counterpart in Xyris. The presence of
the pilate layer, although different in each genus, tends to provide a common
characteristic, as does the rather thick nexine, lacking in lipophilic compounds.
The writer suspects from Erdtman's reports of both "OL" and "LO" sexine
patterns that a layer of united pila may compose the sexine in at least some
Xyris pollen grains. The exine of Achlyphila seems midway between that of
Abolboda and Orectanthe on one hand, and Xyris on the other. The relatively
thick, baculate sexine and the thin nexine of Xyris pollen grains do not seem
at odds with the condition in Achlyphila. Probably the three major patterns
represent striking variations on the same basic pattern. Careful work is needed
both to provide additional data on Xyris and to demonstrate whether the affinity
Erdtman (1952) suggests between the grains of the Abolboda-type and those of
Liliaceae and Zingiberaceae is close or not.
The writer has found that an attempt to summarize anatomical characteristics
of genera of Xyridaceae in chart form is virtually impossible because (1) there are exceptional species within a genus; (2) reference to particular conditions in lengthy anatomical terms, or with the aid of illustrations is necessary; and (3) some relatively subtle characteristics cannot be summarized in this manner. The most important anatomical lines of evidence are cited below, and the reader is referred to the foregoing descriptions, particularly to the "discussion" section terminating each of the major portions above.
Abolboda. Characteristics of leaf anatomy and stem anatomy suggested
recognition of two species-groups, termed here "smaller-stemmed" abolbodas
and "larger-stemmed" abolbodas. ^Recognition of these as subgenera would
probably be premature. Within each of these groupings, leaf and stem anatomy
suggest specific characteristics also. Characteristics other than these do not
emphasize the two species-groups as much as they suggest characteristics of
individual species. The large stele of roots defines A. macrostachya, but genuinely
remarkable specific characteristics are offered by the peculiar patterns of
endodermis-cell thickening. In the inflorescence axis, thickness of selerenchyma
ring, presence of fibrous sheaths on pith bundles, and selerification of epidermal
cells offer a number of characteristics. Distinctive patterns in number of bundles,
size, selerenchyma and chlorench.yma presence and distribution offer further
characteristics in sepals, and, to a lesser extent, in bracts. Perhaps the best
specific characteristics are evident in pollen in such respects as shape and size of
spines, nexine thickness, and diameter.