EFFECTS OF WATER STRESS,ABSCISIC ACID,AND GIBBERELLIC ACID ON FLOWER PRODUCTION AND DIFFERENTIATION IN THE CLEISTOGAMOUS SPECIES COLLOMIA GRANDIFLORA DOUGL. EX LINDL. (POLEMONIACEAE)

The effects of water stress, abscisic acid (ABA), and gibberellic acid (GA₃) on flower production and differentiation by Collomia grandiflora were investigated. An untreated plant typically produced both small, closed cleistogamous (CL) and large, open chasmogamous (CH) flowers. The larger corolla of CH flowers was due to a greater cell number and size. When plants were water-stressed or sprayed with ABA, both the percentage of CH flowers and the total number of flowers were reduced significantly. The corolla dimensions and epidermal cell numbers and sizes of CL flowers produced by water-stressed and ABA-sprayed plants did not differ from those of CL flowers produced by control plants. Application of GA₃ to both well-watered and water-stressed plants significantly increased the percentage of CH flowers formed compared to well-watered controls. In the absence of GA₃, water-stressed plants produced almost entirely CL flowers. GA₃-sprayed plants produced CH flowers whose corolla dimensions were intermediate between those of CL and CH flowers formed by control plants. Epidermal cells of these intermediate corollas were reduced only in number and not in size when compared to control CH flowers. Endogenous levels of ABA and gibberellins may control the type of flower produced by C. grandiflora and may mediate some of the observable effects of water stress on flowering.     

THE BALANCE BETWEEN CHASMOGAMY AND CLEISTOGAMY IN COLLOMIA GRANDIFLORA (POLEMONIACEAE)

The extent of cleistogamy (CL) and chasmogamy (CH) was investigated in natural populations of Collomia grandiflora Dougl. ex Lindl. The ubiquitous occurrence of CL flowers was documented in 18 populations from throughout the geographic range of the species. The interrelationship of environmental perturbation, vegetative weight, and the balance between CH and CL flowers was investigated by means of a factorial experiment which varied plant density, incident light and soil mix. An ANOVA revealed that total plant weight increased significantly under conditions of low density, low light and low sand content, with density accounting for most of the variance in plant weight. Interactions involving density were not significant. The number of CH and CL flowers and estimated percent outcrossing increased significantly with increased plant weight, low density, low light, and low sand content, although an analysis of covariance showed that plant weight and density accounted for most of the variance in these traits. Among large, multibranched plants, the proportion of CL flowers increased in a basipetal pattern, whereas most of the CH flowers were restricted to the terminal and upper inflorescences. The smallest plants produced only a single terminal inflorescence comprising entirely CL flowers. The proportion of reproductive effort allocated to outcrossing was dependent upon plant size as estimated from total weight, whereas the proportion allocated to ***selfing was relatively independent. Studies of outcrossed vs. inbred progenies of five populations revealed little evidence for immediate inbreeding depression with respect to plant weight and the number of CH or CL flowers, but indicated that significant quantitative genetic differences exist for these traits among populations of diverse ecological or geographical origin.     

SEED-COAT MORPHOLOGY AND ANATOMY IN COLLOMIA (POLEMONIACEAE)

Seed-coat morphology of 14 species of Collomia (Polemoniaceae) was examined with light microscopy and scanning electron microscopy. Two seed types were observed based on surface sulpturing: Type 1—hexagonal epidermal cells forming a shallow reticulum with well-defined cell boundaries; Type 2—longitudinally ridged and irregularly arranged crater-like depressions with inconspicuous cell boundaries. Only two species, C. debilis and C. larsenii of sect. Collomiastrum have seed-coat Type 1. Seed-coat Type 2 is characteristic of all species of sect. Collomia, sect. Courtoisia, and C. mazama, C. rawsoniana of sect. Collomiastrum. The present investigation reveals a fairly homogeneous seed-coat pattern in the genus and does not offer significant information for realignment of infrageneric classification. Anatomical studies with light microscopy show that a mucilaginous seed coat develops from the outermost layer of integument in which each epidermal cell develops spiral secondary wall thickenings. Mucilaginous seeds of most Collomia species probably provide adaptive significance in that adherence of seeds to ground prohibits further dispersal to unfavorable habitats, or epizoochoric dispersal.     

VEGETATIVE AND FLORAL RELATIONSHIPS AMONG WESTERN NORTH AMERICAN POPULATIONS OF COLLOMIA LINEARIS NUTTALL (POLEMONIACEAE)

Thirty-seven characters were measured on greenhouse grown progenies of twenty-three populations representing, for Collomia linearis, a broad geographical and ecological distribution in western North America. Twelve vegetative and seventeen floral characters showed significant among-population/within-population variance ratios (F-statistics). Overall, floral characters showed higher F-statistics than did vegetative characters. The F-statistics and character means were used to construct phenograms based on weighted similarity measures and single-linkage clustering. With the exception of a homogeneous cluster comprising northern Rocky Mountain OTUs, relationships based on floral characters were geographically random. No clearly defined morphological trends toward increased autogamy were observed in association with geographical or ecological distribution. Several clustering relationships, based on vegetative characters, were interpreted as representing geographically unrelated genotypes convergent with respect to ecotypic differentiation. The most distinctive clusters of OTUs in the vegetative phenogram were associated with subalpine and wet meadow sites, habitats considered as ecologically marginal for the species. Comparison of the two phenograms revealed considerable disparity between relationships based on floral characters and those based on vegetative characters. This disparity lends support to the hypothesis that floral and vegetative character combinations are subject to independent selective processes. The absence of polyploidy or mitotically detectable chromosomal rearrangements indicates that the observed variation among widely separated populations represents either divergence or convergence via genetic differentiation at the diploid level.     

QUANTITATIVE COMPARISON OF FLORAL DEVELOPMENT IN VERONICA CHAMAEDRYS AND VERONICASTRUM VIRGINICUM (SCROPHULARIACEAE)

Development in Veronica and Veronicastrum was studied to elucidate the growth patterns responsible for differences between their mature flowers. Nineteen floral dimensions were measured on buds from initiation to anthesis, and representative stages were recorded with the scanning electron microscope. Bivariate plots indicate the heterochronic changes responsible for the derived flower form of Veronica. The growth patterns of the gynoecium and androecium were little changed. The calyx of Veronica showed slower size increase at the early stages, but continued to grow after that of Veronicastrum had stopped. The most striking change occurred in the corolla lobes of Veronica, where growth was retarded until the beginning of style formation, but afterward was accelerated relative to that of Veronicastrum. The corolla tube of Veronica remained short due to a later onset of growth and slower enlargement later in development. Multigroup principal components analysis (M-PCA) was used to summarize the measurements. The distribution of points along M-PC 1 describes size increase during floral development. Along M-PC 2 the trajectories of the two taxa diverge after the beginning of style growth, while along M-PC 3 they differ from the earliest stages on, corroborating differences observed with the scanning electron microscope. M-PCA can thus be used to portray differences in patterns of floral development, facilitating simultaneous quantitative comparisons of two or more taxa.     

CONTRIBUTION OF POLLEN MORPHOLOGY TO SYSTEMATICS OF COLLOMIA (POLEMONIACEAE)

Pollen morphology of 14 species of Collomia (Polemoniaceae) was examined by light microscopy, and by both scanning and transmission electron microscopy. Four distinct pollen types were observed which are based principally upon 1) shape, number and distribution of apertures, and 2) surface sculpturing: Type 1—zonocolporate with striate ridges; Type 2—zonocolporate with striato-reticulate ridges; Type 3—pantoporate with radiate ridges; Type 4—pantoporate with irregularly reticulate ridges. Evaluation of pollen morphology reveals considerable discrepancy with respect to presently accepted sectional classification. Collomia grandiflora of sect. Collomia has a pollen type similar to that of members of sect. Collomiastrum and is now interpreted as representing an independent evolutionary line derived from the latter section. Collomia diversifolia of sect. Courtoisia has a pollen morphology similar to that of sect. Collomia. whereas C. heterophylla of the same section possesses pollen unique within the genus. This last pollen type shows close similarity to the pollen of members of Polemonium, Gilia, Leptodactylon, and Ipomopsis. Pollen of C. tinctoria and C. tracyi of sect. Collomia are anomalous within Polemoniaceae. No significant difference in exine stratification was discernible among the four pollen types.     

VARIATION IN SEX ALLOCATION AND FLORAL MORPHOLOGY IN IPOMOPSIS AGGREGATA (POLEMONIACEAE)

Intrapopulational variation in biomass allocation to male vs. female function was quantified for the hermaphroditic plant Ipomopsis aggregata in terms applicable to sex allocation models. The proportions of flower biomass put into the corolla and calyx averaged 0.59 and 0.20 and were relatively constant across plants. The proportions in the stamens and pistil averaged 0.13 and 0.08, with considerable variation among plants. Phenotypic gender at the time of flowering ranged from 0.34 to 0.77 female. Pistil dry weight was correlated with stigma exsertion. Stamen weight was correlated with corolla width, which influences male pollination success, and was also correlated with anther position and pollen production. Female reproductive success as estimated by seeds per flower showed no detectable relationship with initial allocation of biomass at the time of flowering, but decreased in accelerating fashion with the proportion of final biomass including seeds that was allocated to male function.     

QUANTITATIVE VARIATION OF PROGENY FROM CHASMOGAMOUS AND CLEISTOGAMOUS FLOWERS IN THE GRASS DANTHONIA SPICATA

Progeny from chasmogamous (CH) and cleistogamous (CL) flowers of the grass Danthonia spicata were raised in their native habitat and in the greenhouse in order to determine how genetic variation was distributed among families and between CH and CL progeny within families. Twelve quantitative characters were measured on clones from individuals known to have arisen from either CH or CL flowers on a particular plant. Significant genetic variation existed for all characters measured. Most genetic variation was between families and two morphologically similar groups of families were identified. Relatively little genetic variation was found within families (approximately 5% of the total phenotypic variance). In field-raised plants, variance component analysis suggested that CL progeny were genetically more similar to each other than were CH progeny from the same plant. Levene's test of the average deviation of CH and CL progenies from their group means was nonsignificant but suggested there was a trend (0.05 < P < 0.10) for CH progeny to be more variable than CL progeny in the field but less variable in the greenhouse. The amount and distribution of genetic variation in the study population indicates that selective differentials would be larger among families than within families.     

A COMPARISON OF FLORAL DEVELOPMENT IN WILD TYPE AND A HOMEOTIC SEPALOID PETAL MUTANT OF CLARKIA TEMBLORIENSIS (ONAGRACEAE)

The mature wild type petals of Clarkia tembloriensis consist of a long slender claw and an expanded deltoid-shaped limb. They are pink, with a maroon spot at the base of the limb. Their surface texture is smooth. A variant of petal form, crinkled petal, occurs commonly in several natural populations of C. tembloriensis. The mature crinkled petals are elongated, greenish pink, and possess trichomes. They resemble the mature sepals of C. tembloriensis in general shape, color, and surface texture. Organ initiation and subsequent patterns of development of wild type petals, wild type sepals, and crinkled petals were examined and compared using scanning electron microscopy and allometric growth analysis. Crinkled petals are similar to wild type petals in time and position of primordia initiation, and in size and shape at inception. Crinkled petals are similar to wild type sepals in pattern of allometric growth. The crinkled petal mutant fits the broad definition of a homeotic mutant in that the petal has assumed characteristics of the sepal.     

FLORAL DEVELOPMENT IN SAURURUS CERNUUS (SAURURACEAE): 1. FLORAL INITIATION AND STAMEN DEVELOPMENT

The inflorescence of Saururus cernuus L. produces lateral “common” primordia in acropetal succession on the flanks of the inflorescence meristem; curiously, the “subtending” bract is initiated upon the lateral primordium rather than subtending it. On the basis of mature floral structure, flowers of S. cernuus have previously been described as having spiral initiation of parts. The current ontogenetic investigation contradicts this interpretation. Stamens arise in three successive pairs; the carpels also are initiated in pairs. Floral symmetry is shown to be bilateral from the onset of organ initiation, a rare feature among primitive angiosperms. On the basis of symmetry and paired initiation of organs, the possibility of close relationships between Saururaceae and Magnolialian or Ranalian lines appears remote.     

PATTERNS OF FLORAL DEVELOPMENT IN AGALINIS AND ALLIES (SCROPHULARIACEAE). II. FLORAL DEVELOPMENT OF AGALINIS DENSIFLORA

Initiation of floral primordia begins in Agalinis densiflora with production of two lateral adaxial calyx lobe primordia followed by a midadaxial primordium, and then primordia of two abaxial calyx lobes. Initiation of three abaxial corolla lobe primordia is succeeded by that of two stamen pairs and then by primordia of two adaxial corolla lobes. The primordium of the abaxial carpel appears before the adaxial one. Except for the calyx, initiation of primordia proceeds unidirectionally from the abaxial to the adaxial side of the floral apex. Zygomorphy in the calyx, corolla, and androecium is evident during initiation of primordia and is accentuated during organogenesis. The calyx undergoes comparatively rapid organogenesis, but the inner three floral series undergo a protracted period of organogenesis. The perianth series reach maturation prior to meiosis in the anthers. Maturation of the androecium and gynoecium are postmeiotic events.     

DEVELOPMENT OF STRIATE EXINE IN IPOMOPSIS RUBURA (POLEMONIACEAE)

Exine formation in Ipomopsis rubura (L.) Wherry (Polemoniaceae) was traced with transmission and scanning electron microscopy. At the early tetrad stage, plasma membranes of microspores invaginate and form a punctate pattern within the callose wall. Protectum is then deposited, taking a punctate pattern corresponding to the plasma membrane. After dissolution of the callose wall, the punctate pattern develops into a striate sculpture by partial thickening of tectum. The mature tectum is thus composed of two layers, the inner punctate and outer striate layers. With the plasma membrane determining the initial tectum pattern within the tetrad, additional sculptural elements are later formed above this pattern during the free microspore stage.     

FLORAL DEVELOPMENT AND VASCULATURE IN HYDROCLEIS NYMPHOIDES (BUTOMACEAE)

The flower of Hydrocleis nymphoides consists of three sepals which arise in spiral succession, three simultaneously arising petals, numerous stamens and staminodia which arise in centrifugal order, and six carpels. A residual apex remains at maturity. The first-formed members of the androecium are stamens and the later-formed members are staminodia which develop below the stamens and which become outwardly displaced during expansion of the receptacle. The androecium is supplied by branching vascular trunk bundles. The carpels are completely open but the ventral margins are slightly conduplicately appressed basally. A single dorsal bundle provides the stigmatic area with vascular tissue, and a network of small placental bundles supplies the numerous laminar ovules. There are no clearly defined ventral bundles. It is suggested that Hydrocleis nymphoides is neither the most primitive nor the most advanced member of the family. A pattern of phylogenetic reduction in the androecium and receptacle is suggested for the entire family.     

INFLORESCENCE AND FLORAL DEVELOPMENT IN HOUTTUYNIA CORDATA (SAURURACEAE)

The inflorescence of Houttuynia cordata produces 45–70 sessile bracteate flowers in acropetal succession. The inflorescence apical meristem has a mantle-core configuration and produces “common” or uncommitted primordia, each of which bifurcates to form a floral apex above, a bract primordium below. This pattern of organogenesis is similar to that in another saururaceous plant, Saururus cernuus. Exceptions to this unusual development, however, occur in H. cordata at the beginning of inflorescence activity when four to eight petaloid bract primordia are initiated before the initiation of floral apices in their axils. “Common” primordia also are lacking toward the cessation of inflorescence apical activity in H. cordata when primordia become bracts which may precede the initiation of an axillary floral apex. Many of these last-formed bracts are sterile. The inflorescence terminates with maturation of the meristem as an apical residuum. No terminal flowers or terminal gynoecia were found, although subterminal gynoecia or flowers in subterminal position may overtop the actual apex and obscure it. Individual flowers have a tricarpellate syncarpous gynoecium and three stamens adnate to the carpels; petals and sepals are lacking. The order of succession of organs is: two lateral stamens, median stamen, two lateral carpels, median carpel. The three carpel primordia almost immediately are elevated as part of a gynoecial ring by zonal growth of the receptacle below the attachment of the carpels. The same growth elevates the stamen bases so that they appear adnate to the carpels. The trimerous condition in Houttuynia is the result of paired or solitary initiations rather than trimerous whorls. Symmetry is bilateral and zygomorphic rather than radial. No evidence of spiral arrangement in the flower was found.     

FLORAL DEVELOPMENT IN MYRISTICA (MYRISTICACEAE)

Myristica fragrans and M. malabarica are dioecious. Both staminate and pistillate plants produce axillary flowering structures. Each pistillate flower is solitary, borne terminally on a short, second-order shoot that bears a pair of ephemeral bracts. Each staminate inflorescence similarly produces a terminal flower and, usually, a third-order, racemose axis in the axil of each pair of bracts. Each flower on these indeterminate axes is in the axil of a bract. On the abaxial side immediately below the perianth, each flower has a bracteole, which is produced by the floral apex. Three tepal primordia are initiated on the margins of the floral apex in an acyclic pattern. Subsequent intercalary growth produces a perianth tube. Alternate with the tepals, three anther primordia arise on the margins of a broadened floral apex in an acyclic or helical pattern. Usually two more anther primordia arise adjacent to each of the first three primordia, producing a total of nine primordia. At this stage the floral apex begins to lose its meristematic appearance, but the residuum persists. Intercalary growth below the floral apex produces a columnar receptacle. The anther primordia remain adnate to the receptacle and grow longitudinally as the receptacle elongates. Each primordium develops into an anther with two pairs of septate, elongate microsporangia. In pistillate flowers, a carpel primordium encircles the floral apex eventually producing an ascidiate carpel with a cleft on the oblique apex and upper adaxial wall. The floral ontogeny supports the morphological interpretation of myristicaceous flowers as trimerous with either four-sporangiate anthers or monocarpellate pistils.     

IRREGULAR FLORAL DEVELOPMENT IN CALLA PALUSTRIS (ARACEAE) AND THE CONCEPT OF HOMEOSIS

About two-thirds of the more than 100 genera in the Araceae lack tepals and their absence is considered derived. Unlike most of these atepalate genera, Calla palustris has about twice as many stamens per flower. Using epi-illumination microscopy, we studied floral development in Calla to see if the supernumerary stamens form in positions corresponding to tepal positions in perigonate Araceae. If so, this would be an example of homeosis—in this case, the replacement of tepals with stamens—in the evolution of this genus. We found the positions of stamen primordia in many floral buds too irregular to conclude that they replace tepals positionally. However, in more regular floral buds the first formed stamens do form in what correspond to tepal sites in related genera. If the immediate ancestor to Calla had tepals, as is generally assumed, stamen positions in the more regular flowers, at least, support a homeotic interpretation. There is no evidence that the supernumerary stamens arise by dédoublement, but since morphogenesis in Calla is only partly comparable to other aroids, and the phylogeny in the family is not well understood, further studies are needed to resolve the interpretation of the flower in Calla. With regard to systematics and evolution, the absence of tepals in Calla may not be homologous with atepaly in other members of the family, as has been assumed for the past century.     

FLORAL DEVELOPMENT IN CAESALPINIA (LEGUMINOSAE)

Utilizing scanning electron microscopy, we studied the early floral ontogeny of three species of Caesalpinia (Leguminosae: Caesalpinioideae): C. cassioides, C. pulcherrima, and C. vesicaria. Interspecific differences among the three are minor at early and middle stages of floral development. Members of the calyx, corolla, first stamen whorl, and second stamen whorl appear in acropetal order, except that the carpel is present before appearance of the last three inner stamens. Sepals are formed in generally unidirectional succession, beginning with one on the abaxial side next to the subtending bracts, followed by the two lateral sepals and adaxial sepal, then lastly the other adaxial sepal. In one flower of C. vesicaria, sepals were helically initiated. In the calyx, the first-initiated sepal maintains a size advantage over the other four sepals and eventually becomes cucullate, enveloping the remaining parts of the flower. The cucullate abaxial sepal is found in the majority of species of the genus Caesalpinia. Petals, outer stamens, and inner stamens are formed unidirectionally in each whorl from the abaxial to the adaxial sides of the flower. Abaxial stamens are present before the last petals are visible as mounds on the adaxial side, so that the floral apex is engaged in initiation of different categories of floral organs at the same time.     

NORMAL FLORAL ONTOGENY AND COOL TEMPERATURE-INDUCED ABERRANT FLORAL DEVELOPMENT IN GLYCINE MAX (FABACEAE)

Floral onset in soybean (Glycine max cv. Ransom) is characterized by precocious initiation of axillary meristems in the axils of the most recently initiated leaf primordium. During floral transition, leaf morphology changes from trifoliolate leaf with stipules, to a three-lobed bract, to an unlobed bract. Soybean flowers initiated at 26/22 C day/night temperatures are normal, papilionaceous, and pentamerous. Sepal, petal, and stamen whorls are initiated unidirectionally from the abaxial to adaxial side of the floral apex. The median sepal is located abaxially and the median petal adaxially on the meristem. The organogeny of ‘Ransom’ flowers was found to be: sepals, petals, outer stamens plus carpel, inner stamens; or, sepals, petals, carpel, outer stamens, inner stamens. The outer stamen whorl and the carpel show possible overlap in time of initiation. Equalization of organ size occurs only within the stamen whorls. The sepals retain distinction in size, and the petals exhibit an inverse size to age relationship. The keel petals postgenitally fuse along part of their abaxial margins; their bases, however, remain free. Soybean flowers initiated at cool day/night temperatures of 18/14 C exhibited abnormalities and intermediate organs in all whorls. The gynoecium consisted of one to ten carpels (usually three or four), and carpel connation varied. Fusion of keel petals was often lacking, and stamen filaments fused erratically. Multiple carpellate flowers developed into multiple pods that were separate or variously connate. Intermediate type organs had characteristics only of organs in adjacent whorls. These aberrant flowers demonstrate that the floral meristem of soybean is not fixed or limited in its developmental capabilities and that it has the potential to produce alternate morphological patterns.     

FLORAL INITIATION AND EARLY DEVELOPMENT IN ERIGERON PHILADELPHICUS (ASTERACEAE)

The order of floral initiation and subsequent organogeny of Erigeron philadelphicus L. (Asteraceae: Astereae) was found to deviate from the acropetal pattern generally reported for the Asteraceae. Light micrographs show periclinal divisions in the first, second, and deeper subsurface layers of cells on the flanks of the inflorescence apex as the earliest evidence of floral initiation. Scanning electron microscope micrographs indicate that the disk flowers appear first and arise as small protuberances approximately one-third of the way up the previously and undifferentiated highly convex inflorescence apex. A succession of disk flowers arises acropetally in a complex anthotaxy characterized by about 21 dextrorse and 12–15 sinistrorse parastichies (although this pattern is obscured at the apex). After one to three disk flowers have been initiated in each parastichy, the first ray flower initials can be seen to initiate in sites proximal to the oldest and largest disk flowers. Additional ray flowers then initiate basipetally following the dextrorse parastichies established by the disk flowers. Overall floral initiation on the inflorescence apex proceeds acropetally for the disk flowers and basipetally for the ray flowers until the available space is filled. Floral development adheres to the same plan—proceeding bidirectionally on the inflorescence meristem with the oldest and most complete flowers of both types located on the equator established at initiation.