COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. I. PRUNOIDEAE: PRUNUS

A study of the carpel in 27 species of Prunus has shown certain notable structural relationships associated with the extent of closure of the carpellary margins. These relationships involve the degree of fusion of the 2 integuments, the number of vegetative bundles in the base of the carpel, the extent of fusion of the ovular bundles with one another and with the wing bundles, the relative size of the ovular bundles, and the relative development of the central vascular plexus. The comparative evidence strongly supports a primitively separate state of ovular and vegetative bundles. The significance of this finding is discussed.     

THE AFFINITIES OF PRINSEPIA (ROSACEAE)

Sterling, C. (U. California, Davis.) The affinities of Prinsepia (Rosaceae). Amer. Jour. Bot. 50(7): 693–699. Illus. 1963.—Anatomical study of the carpels of 4 species of Prinsepia has shown that at flowering the 2 ovules are erect and pleurotropic. The funiculus is on the dorsal and lower side of the ovule; the micropyle faces a large obturator on the ventral side. The carpellary margins are separated by a fissure below the funicular insertion, but above this level they are fused. The style is laterally inserted on the ventral face of the carpel; it is vascularized only by the wing bundles and the recurving dorsal bundle. At the base of the ovary, 2 ovular bundles depart from the vascular cylinder and run separately, each to its respective ovule. In carpel morphology, ovular position, ovule structure, and vascular anatomy, Prinsepia is not a prunoid type. Although its features on the whole resemble those of chrysobalanoid plants, there are notable differences. Consequently, Prinsepia is assigned to a new subfamilial group in the Rosaceae, the Prinsepioideae. Some phylogenetic considerations are discussed briefly.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE VI. POMOIDEAE: ERIOBOTRYA,HETEROMELES, PHOTINIA,POURTHIAEA, RAPHIOLEPIS,STRANVAESIA

The pomoid genera, Eriobotrya, Photinia, Pourthiaea, Raphiolepis, Stranvaesia, and Heteromeles, have compound inflorescences and biovulate carpels which become papery at maturity. The carpels of all of these except Heteromeles are fused with one another. There are open sutures in the carpels of Heteromeles, Photinia, Pourthiaea, and Raphiolepis, and in these four genera the extent of fusion of the ovular bundle with the wing bundle is related directly to the state of tegumentary fusion and to the extent of fusion of the carpel with the floral cup. In those species of Eriobotrya and Stranvaesia with closed sutures the integuments tend to be fused, as do the ovular and wing bundles, and the carpels are adnate with the floral cup for a considerable distance; in species with open sutures the integuments tend to be free, the ovular and wing bundles tend to be separate, and the extent of fusion of carpel with floral cup tends to be shorter. In genera with connate carpels the wing bundles of adjoining carpels may also be fused. The greatest extent of fusion occurs in Eriobotrya and Raphiolepis, in which there may also be attenuation and disappearance of the wing bundles above the region of ovular insertion and even reduction and disappearance of the carpellary margin.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. IV. POMOIDEAE: CHAMAEMELES,COTONEASTER, DICHOTOMANTHES,PYRACANTHA

The carpels of Chamaemeles, Cotoneaster, Dichotomanthes, and Pyracantha tend to be separate from one another, their sutures tend to be closed, and they become more or less bony at maturity. However, aside from having collaterally placed ovules, they do not appear to be structurally similar. There seem to be 2 different evolutionary trends in the ovular bundle–wing bundle relationship: in Pyracantha, progressive fusion between the ovular bundle and the wing bundle has led to the formation of a “ventral” bundle; in Cotoneaster, and possibly Chamaemeles, the wing bundle has become reduced and rather attenuated. A primitive pomoid state may be represented by the carpel of Dichotomanthes, which is completely free of the floral cup and in which wing and ovular bundles are separate. Differences in sutural closure appear only in Cotoneaster, and in species of that genus the wing bundles and ovular bundles tend to be fused if the suture is closed, and separate if it is open.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE VII. POMOIDEAE: CHAENOMELES,CYDONIA, DOCYNIA

The multi-ovulate pomoids, Chaenomeles, Cydonia, and Docynia, all have closed sutures and extensive fusion between carpel and floral cup and between ovular and wing bundles. Although the ovules in Docynia are generally apotropic and few in number (4–7), the ovules in the other two genera are pleurotropic and numerous (15–48). A statistical treatment of the whole tribe of Pomoideae shows that in carpels with open sutures ovular and wing bundles definitely tend to be separate while in those with closed sutures these bundles tend to be fused. To a lesser degree carpels with open sutures also tend to have bitegmic ovules, separate carpels, and a lesser extent of fusion between carpel and floral cup, while carpels with closed sutures tend to have monotegmic ovules, united carpels, and a greater extent of fusion between carpel and floral cup.     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. III. POMOIDEAE: CRATAEGUS,HESPEROMELES, MESPILUS,OSTEOMELES

The carpels in Crataegus, Hesperomeles, Mespilus, and Osteomeles appear to constitute a morphologically related group: all have bony pits, ovules that tend to be acollateral (usually superposed), and clearly separate ovular and wing bundles, i.e., no “ventral” bundles, at the level of ovular insertion. In species whose carpels have no sutural opening, the integuments are more extensively fused with one another, the degree of intercarpellary fusion tends to be greater, and the carpels are fused with the floral cup to relatively higher levels than in those species whose carpels have a sutural opening. In the few cases in which wing and ovular bundles are adnate at the locular base (Crataegus monogyna, Mespilus, Osteomeles anthyllidifolia, O. Schwerinae), the extent of inter- and extracarpellary fusion and sutural closure is among the most advanced.     

STUDIES ON THE FLORAL ANATOMY OF THE CUNONIACEAE

Twenty-two genera representing sixty-two species of Cunoniaceae and Davidsonia were examined with respect to floral anatomy. Sepals are vascularized by three traces with the lateral traces of adjacent sepals united. Pancheria is unique for the family with species in which the sepals are vascularized by a single, undivided bundle. Petals, when present, and stamens, are uniformly one-trace structures. A general tendency exists within the family for the principal floral bundles to unite in various ways, with fusions evident between calyx, corolla, and androecial vascular supplies. Carpel number ranges from two to five and the gynoecium is generally surrounded by a prominent disc. Gynoecia of Ceratopetalum and Pullea are “half-inferior.” The number of ovules per carpel locule ranges from one to numerous. Ventral carpel sutures range from open to completely sealed at the level of placentation. Carpels of the apocarpous genus Spiraeanthemum (incl. Acsmithia) are vascularized by a dorsal bundle and either three or four bundles constituting the ovular and wing vasculation in the ventral position, a condition unlike other members of the family. Ovules are supplied by the median ventral bundle. More advanced bicarpellate gynoecia within the family are predominately vascularized by a dorsal and two ventral bundles although a variable number of additional lateral wall traces may be present. A major trend exists toward fusion of the ventral bundles of adjacent carpels in the ovary of both bicarpellate and multicarpellate plants. At the base of the styles the fused ventral strands separate and extend along with the dorsal carpellary bundles into styles of adjacent carpels. In Pullea the ventral bundles terminate within the ovules. The united ventral carpellary bundles in Aphanopetalum, Gillbeea, and Aistopetalum lie in the plane of the septa separating adjacent carpels. Ovules are vascularized by traces originating from the vascular cylinder at the base of the gynoecium or by traces branching from the ventral bundles. Ovular traces in each carpel are united, or remain as discrete bundles, prior to entering the placenta. Tannin and druses are common throughout all floral parts. Although floral anatomy generally supports the position of Cunoniaceae near Saxifragaceae and Davidsoniaceae, the evolutionary relationship of the Cunoniaceae to the Dilleniaceae is uncertain.     

THE MORPHOLOGY OF THE MYRISTICACEAE. I. FLOWERS OF MYRISTICA FRAGRANS AND M. MALABARICA

Floral histology and vascular anatomy of Myristica fragrans Van Houtt. and M. malabarica Lam. have been investigated from serial sections and specimens cleared in chloro-lacto-phenol. The flowers are unisexual. The androecium is considered to consist of a whorl of laterally concrescent anthers. The bisporangiate anthers are attached by a ridge of tissue to the terminal part of the androphore. In many cases the number of vascular bundles in the androphore is half the number of anthers. The gynoecium consists of a monocarpellate pistil with basal placentation and a single anatropous ovule. Of the many vascular bundles that enter the base of the carpel, two, because of their position and because they provide vascular traces to the ovule, are designated as ventral bundles. Additional ovular traces are provided by the carpel wall vascular system. These additional traces originate at the top of the locule and descend to the ovule. The similarity between the androecia of these two species and the androecium of the ćnellaceae is noted.     

MORPHOLOGICAL STUDIES OF THE NYMPHAEACEAE SENSU LATO. XVII. FLORAL ANATOMY OF ONDINEA PURPUREA SUBSPECIES PURPUREA (NYMPHAEACEAE)

Classification and phylogeny of the Nymphaeaceae are unresolved. This study provides floral anatomical data that will assist in elucidating generic interrelationships and systematic relationships to other taxa of angiosperms. The floral anatomy of Ondinea purpurea den Hartog subsp. purpurea has been examined utilizing light microscopy. The peduncle possesses stelar vascular bundle complexes and cortical vascular bundles. Cortical bundles terminate within the peduncle. Each bundle complex consists of 2 collateral bundles on the same radius, the inner bundle inverted; 2 protoxylary lacunae occur yet differ in structure and function. Progressing acropetally, the inner xylary lacunae become discrete mesarch strands surrounded centrifugally by a vascular cylinder formed by divisions and anastomosing of the bundle complexes. Together these become the massive receptacular vascular plexus. The plexus provides collateral traces to the floral organs. Each sepal receives 3 traces that separate from the plexus as 1–3 lateral traces. Petals are absent and no vestigial petal traces have been observed. Distally, the plexus forms several large strands of connate gynoecial and androecial traces termed the principal vascular bundles (PVBs). Ventral veins separate from the PVBs and the latter extend acropetally through the outer ovary wall. Branches of the ventrals and PVBs contribute to septal vascular reticula from which each ovule is supplied by one vascular bundle. Each stamen receives 1 trace from branches of the PVBs. The ventrals and PVBs terminate within the carpellary lobes. A comparative anatomical study is offered that supports the inclusion of Ondinea in the Nymphaeaceae sensu stricto.     

Expression-based discovery of candidate ovule development regulators through transcriptional profiling of ovule mutants

Background  

Arabidopsis ovules comprise four morphologically distinct parts: the nucellus, which contains the embryo sac, two integuments that become the seed coat, and the funiculus that anchors the ovule within the carpel. Analysis of developmental mutants has shown that ovule morphogenesis relies on tightly regulated genetic interactions that can serve as a model for developmental regulation. Redundancy, pleiotropic effects and subtle phenotypes may preclude identification of mutants affecting some processes in screens for phenotypic changes. Expression-based gene discovery can be used access such obscured genes.     

Expression of ovule and integument‐associated genes in reduced ovules of Santalales

SUMMARY Santalales comprise mainly parasitic plants including mistletoes and sandalwoods. Bitegmic ovules similar to those found in most other angiosperms are seen in many members of the order, but other members exhibit evolutionary reductions to the unitegmic and ategmic conditions. In some mistletoes, extreme reduction has resulted in the absence of emergent ovules such that embryo sacs appear to remain embedded in placental tissues. Three santalalean representatives (Comandra, Santalum, and Phoradendron), displaying unitegmic, and ategmic ovules, were studied. Observed ovule morphologies were consistent with published reports, including Phoradendron serotinum, which we interpret as having reduced ategmic ovules, consistent with earlier reports on this species. For further understanding of the nature of the ovule reductions we isolated orthologs of the Arabidopsis genes AINTEGUMENTA (ANT) and BELL1 (BEL1), which are associated with ovule development in this species. We observed ovular expression of ANT and BEL1 in patterns largely resembling those seen in the integumented ovules of Arabidopsis. These genes were found to be expressed in the integument of unitegmic ovules and in the surface layers of ategmic ovules, and in some cases, expression of BEL1 was also observed in the surrounding carpel tissue. We hypothesize that ategmic ovules derive from a fusion of the integuments with the nucellus or that the nucellus has taken on some of the characteristics confined to integuments in ancestral species.     

VASCULAR SUPPLY AND STRUCTURE OF THE OVULE AND ARIL IN PEONY AND OF THE ARIL IN NUTMEG

Camp , Wendell H., and Mary M. Hubbard . (U. Connecticut, Storrs.) Vascular supply and structure of the ovule and aril in peony and of the aril in nutmeg. Amer. Jour. Bot. 50(2): 174–178. Illus. 1963.—Examination of the placental region in the carpel of Paeonia indicates a complexity and super-abundance of vascular supply beyond that usually found in angiosperms and certainly more than is necessary for adequate nutrition and water supply of the ovules. From this it is concluded that the ovules once were borne on a larger and more complex structure than the present carpel. Vascular strands leading to the aril and the hypostase are interpreted as being relictual. The large multifid aril of Myristica has a well-developed vascular system composed of several sizes of branched bundles.     

FLORAL ONTOGENY OF ILLICIUM FLORIDANUM,WITH EMPHASIS ON STAMEN AND CARPEL DEVELOPMENT

The ontogeny of the flower and fruit of Illicium floridanum Ellis, the Star Anise, was investigated. Each of 5 or 6 bracts in each mixed terminal bud subtends either a vegetative or floral bud. The solitary flowers occur in terminal or axillary positions. Each flower has 3–6 subtending bracteoles arranged in a clockwise helix. The flowers in our material have 24–28 tepals, 30–39 stamens, and usually 13 (rarely 19) uniovulate carpels. Tepals and stamens are initiated in a low-pitched helix; carpels later appear whorled, but arise successively at different levels on the apical flanks. The floral apex is high-convex in outline with a tunica-corpus configuration; it increases in height and width throughout initiation of the floral appendages. Tepals, stamens, and carpels are initiated by one to several periclinal divisions in the subsurface layers low on the apical flanks, augmented by cell divisions in the outer layers of the corpus. The carpel develops as a conduplicate structure with appressed, connivent margins. Procambium development of floral appendages is acropetal and continuous. Bracteoles, tepals, stamens and carpels are each supplied by 1 trace; the carpellary trace splits into a dorsal and an ascending ventral sympodium. The latter bifurcates to form 2 ventral bundles. The ovular bundle diverges from the ventral sympodium. Ovule initiation occurs in a median axillary position to the carpel, an unusual type of ovule initiation. The fruit vasculature is greatly amplified as the receptacle and follicles enlarge. After carpel initiation an apical residuum persists which is not vascularized; a plate meristem develops over its surface to produce a papillate structure.     

Le Basi Anatomiche Dei Rapporti Nutritivi Tra Pianta Madre,Seme Ed Embrione

Abstract

The anatomical basis of the nutritive relationships between mother plant, seed, and embryo. — The morphology and anatomy of the fruits and seeds of the Angiosperms show a great variety of structures and adaptments, even within the same family, and one must be cautious in drawing generalized conclusions.

If we first examine the ovary we see that the single carpel receives three vascular traces from which the three main bundles originate, a dorsal and two ventral ones, all more or less reduced. Except in the case of laminar placentation the ovule traces are connected to the ventral vascular system, but often the entire vascular system of the ovary is anastomosed and therefore reticular. However especially when the placentae are at the centre or at the basis of the ovary, it is possible to detect a tendency towards a separation between the vascular system of the ovarian wall and that of the placentae.

The ovular bundle runs through the funicle reaching the chalaza, where it can either end or continue towards the micropyle with a single bundle or with a few branches or even forming a complete reticular envelope surrounding the ovule. The ovular vascular bundles are normally found in the outer integument.

The ovule is made of an inner part (nucellus), and an outer one (integuments). The integuments play a very important role in the processes of seed maturation, dormancy, and germination. They are isolated from the interior of the seed by a cuticle which is a common production of the inner integumentary epidermis, and of the nucellus. The cuticle is not present in the chalaza and can be dissolved in the micropylar region: through these two apertures nutrients can penetrate into the seed or haustoria can grow out of it. During the course of maturation these openings become closed by various means, often through the formation of a new cuticle or of a suberised chalazal plate.

The nutrients which pass through the chalaza penetrate into the nucellus where in some cases one can find some structures which facilitate the communications between the chalaza and embryo sac. The endosperm feeds at the expense of the nucellus but often it can establish a direct contact with the chalaza or the integuments or even the placentae. This occurs often thanks to haustoria.

The embryo is normally surrounded at first by a more or less liquid endosperm: in a second stage the endosperm becomes cellular and the embryo grows at its expense through the digestive activity of the cotyledonar epidermis.

From an anatomo-physiological point of view the following points seem of particular interest:

(I) The endosperm and the embryo show a remarkable autonomy in respect of the mother plant: from an anatomical point of view this is shown by the isolation of the endosperm and embryo by means of a cuticular covering or substitutive structures and by the interposition of nutritive tissues between the vascular system of the mother plant and the endosperm.

(II) Given the importance of the inner cuticle its presence and its constitution should be ascertained in the various species having also in mind the properties of selective permeability shown by the testa.

(III) Two nutritive mechanisms exist: translocation of nutrients via the vascular system and the nutritive tissues, and digestion of surrounding cells. In the digestive phenomena it is important to explain the mechanisms by which only the right cells are digested and not the others.

(IV) The embryo very frequently is immersed at first in a more or less liquid endosperm and is later surrounded by a compact tissue; the nutritive mechanisms are probably different in the two cases.

(V) Two endospermic zones are often distinguishable: one having an haustorial or at least a digestive or elaborative function, and being typically non cellular; another zone, typically cellular, forms a tissue which is sooner or later absorbed by the embryo. The cellularization of this zone seems to coincide with the establishment of polarity and with the beginning of maximum growth of the embryo.

(VI) The relationships between the inner seed and the integuments is complex and there is a correlation between the histoanatomical and biochemical changes of these two parts during seed development. The modifications undergone by the integuments are important steps also towards the preparation of the seed to the processes of dispersal, dormancy, and germination.     

Comparative morphology of the carpel in the Liliaceae: Glorioseae

The pistils of the Glorioseae (Gloriosa, Littonia, Sandersonia) are generally tricarpellate and alike. Virtually all have closed sutures at flowering; they have many ovules, some of which are barely bitegmic, with inner integuments often nearly fused with nucellar remnants; and there is usually but one compound septal bundle in the inner edge of a septum. In two species of Littonia , the compound septal bundle divided to form two simple septal bundles; but in many other plants it remained undivided, and in some it died out, still undivided, below the locular apex. Most of the placental and septal bundles are vascularized in large part by three alternate (compound septal) bundles at the base of the locules and sometimes by branches from the lateral bundles. Three large (compound) placental bundles are formed just below the lowermost ovular insertion, and each then divides in two to furnish ovular branches along their ascent. Occasional auxiliary placental bundles lie between the septal bundle and the placental bundles in the septum (Gloriosa, Sandersonia).     

COMPARATIVE MORPHOLOGY OF THE CARPEL IN THE ROSACEAE. V. POMOIDEAE: AMELANCHIER,ARONIA, MALACOMELES,MALUS, PERAPHYLLUM,PYRUS, SORBUS

The carpels of 2 groups of pomoid genera, Amelanchier, Malacomeles, Peraphyllum and Aronia, Malus, Pyrus, and Sorbus, were analyzed morphologically. Open sutures are associated with a lesser extent of tegumentary fusion and ovular bundle–wing bundle fusion than are closed sutures. However, in the genera as a whole (and particularly in Aronia and Sorbus), the extent of sutural closure is inversely related with the amount of intercarpellary adhesion and with the fusion of carpels to the floral cup. In the Amelanchier group and in Malus and Pyrus, ovular- and wing-bundle fusion is directly related with intercarpellary adhesion. Malus and Pyrus have closer structural resemblances with one another than they have with Aronia and Sorbus.     

POSTGENITAL CARPEL FUSION IN CATHARANTHUS ROSEUS (APOCYNACEAE) IV. SIGNIFICANCE OF THE FUSION

The ontogenetic and phylogenetic significances of the postgenital carpel fusion in Catharanthus roseus were investigated experimentally. When one of the two carpel primordia was surgically destroyed prior to carpel fusion, the remaining carpel differentiated nevertheless; however, the tissue development on the adaxial (normally fused) carpel face appeared aberrant. Possible reasons for this modified ontogeny are discussed. The suggestion that syncarpy is phylogenetically significant because any pollen tube can potentially reach any ovule was verified in C. roseus by monitoring pollen tube growth following spatially controlled pollinations. The suture formed by the postgenital fusion was no barrier to pollen tube growth, and the pollen tubes rapidly became distributed throughout the stigmatic tissue.     

FLORAL ANATOMY IN THE SAXIFRAGACEAE SENSU LATO. II. SAXIFRAGOIDEAE AND ITEOIDEAE

The floral anatomy and morphology of 26 species from the Saxifragoideae and three from the Iteoideae are described and compared. The flowers of the Saxifragoideae are predominantly actinomorphic, partially epigynous and/or perigynous, and pentamerous, with two carpels which bear numerous ovules. There is usually some degree of independence between carpels, and the normally separate styles possess both a canal and transmitting tissue. Generally, staminodia are absent and nectariferous tissue, which is not vascularized, is present. The subfamily is characterized by large multicellular trichomes with globular, often glandular, heads. Placentation may be parietal, axile, or transitional between the two; parietal appears to be a derived condition in the subfamily. The vascular cylinder in the pedicel generally consists of several to many discrete bundles from which diverge ten compound traces at the base of the receptacle, leaving an inner cylinder of vascular strands that coalesce at a higher level into either as many ventral bundles as carpels or twice that number. In the former case, each ventral bundle consists of one-half of the vascular supply to each adjacent carpel and separates into individual ventral strands in the distal half of the ovary. The ventral bundles provide vascular traces to the ovules and, along with the dorsals, extend up the style to the stigma. Each trace diverging in a sepal plane typically supplies one or more carpel-wall bundles, a median sepal bundle, and a stamen bundle. Each petal-plane trace usually provides one or more carpel-wall bundles, a lateral trace to each adjacent sepal, a petal bundle and, in flowers with ten stamens, a stamen bundle. Dorsal carpel bundles are usually recognizable and may originate from traces in either perianth plane. While the position of Ribes remains problematical, its floral structure does not easily exclude it from the Saxifragoideae. Floral structure in the Iteoideae is remarkably similar to that in the Saxifragoideae, the main differences being a lesser degree of independence between carpels, generally narrower placentae with somewhat fewer ovules, and the presence of only unicellular, acutely pointed epidermal hairs as opposed to the relatively complex, multicellular trichomes prevalent in the Saxifragoideae.     

FLORAL MORPHOLOGY OF HORSFIELDIA (MYRISTICACEAE)

The pistillate flowers of Horsfieldia are morphologically similar to those of Myristica and Knema, and are composed of a single whorl of thick, fleshy tepals, and an unsealed, monocarpellate pistil bearing a single ovule. The carpel is vascularized by two ventral bundles, a pair of dorsal bundles, and several supernumerary bundles. The ovule vascularization is derived from the supernumerary bundles. Paired dorsal vascular bundles are an uncommon feature of uncertain significance. Carpels of Myristica and Knema lack any clearly defined dorsal vasculature, and the ovule vascular supply is derived from both the ventral and supernumerary bundles. The organization of the staminate flowers of Horsfieldia agrees with the myristicaceous pattern observed in Myristica and Knema. Each androecium consists of a single whorl of anthers fused or partially fused to a massive connective column. Each anther consists of a pair of bisporangiate lobes and a single vascular bundle. The androecial forms observed are interpreted as forming a series of intermediates between the monadelphous type of androecia of two South American genera, Compsoneura and Dialyanthera, and one African genus, Brochneura, and the solid, columnar androecia which are predominate in the family. Accumulating evidence supports a proposed South American or west Gondwanaland origin of the Myristicaceae.     

VASCULAR SYSTEM OF THE FLORET OF LEERSIA VIRGINICA (GRAMINEAE-ORYZOIDEAE)

The vascular system of the floret of Leersia is unified yet is segmented according to the appendages it serves. The rachilla at the floret base contains a collateral bundle related to the median trace of the lemma. The palea median trace joins the posterior of this bundle in the rachilla as the lemma laterals merge with the anterior. Although the stamen traces enter at the flanks of this rachilla bundle, they do not become fully incorporated into the system until near the floret base where the rachilla bundle, lemma laterals, and palea laterals converge. Traces from the lodicules attach to the anterior of the stamen traces. The base of the vascular system of the pistil, the pistil plexus, attaches tenuously by a bundle to the lower system between the entrance of the stamen traces. A bundle from each style attaches near the anterior of the pistil plexus below the level where the posterior of the pistil plexus rises, as the placental bundle, to merge with the ovule. Characteristics of the vascular system of Leersia, such as the relative discreteness of the staminal and stylar traces and the lack of both the anterior pistil bundle and the xylem discontinuity, are useful for delimiting the Oryzoideae from the Festucoideae.