Stigma Width Research Articles

Relationship between Flower Phenotypic Traits and Fruit Yields in Tea (Camellia sinensis L.) Varieties

In order to provide early selection indicators for the breeding of plants used for producing tea seed oil or harvesting tea, we investigated the relationships between flower morphology and fruit yields in tea plants. We analyzed 106 tea varieties to determine the relationships between flower morphological traits and fruit yields. Notably, the homogeneity of flower traits within the same tea plant variety was found to be very high. The average length and width measurements of certain phenotypic traits of tea plants, including pistil length, stamen length, stamen bundle inner width, stamen bundle outer width, and stigma width, were 11.8, 10.9, 2.5, 15.0, 3.7 mm, respectively. In this study, the flower traits that affect fruit yield appear to be related to the difficulty of pollination by insects (e.g., bees), in terms of their contacting the stigma. In 2013, three phenotypic trait variables showed significant effects on yield; namely, the stamen bundle outer width (negative), stigma width (positive), and stigma width minus the stamen bundle inner width (positive). In 2015, only the stamen bundle outer width had a significant negative effect on yield. Regarding pollen viability, in the TTC (2,3,5-triphenyl tetrazolium chloride) staining test, about 84% of the considered tea varieties presented pollen viability exceeding 70%. This indicates that most tea pollen has the ability to germinate normally after contact with the cross-pollinated stigma. The yields of all of the tea varieties exhibited a positively skewed distribution in 2013 and 2015. Although our results indicate that flowers in the anther superior group tend to produce fewer fruits than flowers in the stigma superior group in 2013, in the analysis of the effect of traits on yield, there were no significant differences in the relative positions of stigmas and anthers. In conclusion, we determined that the main trait affecting fruit yield is stamen bundle outer width, while the secondary trait affecting fruit yield is stigma width. However, the efficacy of the stigma width may also be affected by the position of the stigma relative to the anther and the stamen bundle inner width. These two traits have the potential to be used as reference indicators for early selection in future breeding programs.

Cyanobacteria Application Ameliorates Floral Traits and Outcrossing Rate in Diverse Rice Cytoplasmic Male Sterile Lines.

In rice, cytoplasmic male sterility (CMS) represents an irreplaceable strategy for producing high-yielding hybrid rice based on the commercial exploitation of heterosis. Thereupon, enhancing floral traits and outcrossing rates in CMS lines increase hybrid seed production and ensure global food security. The exogenous application of cyanobacteria could enhance outcrossing rates in CMS lines and, accordingly, hybrid rice seed production. In the present study, we aimed at exploring the impact of cyanobacteria implementation such as Anabaena oryzae, Nostoc muscorum, and their mixture to promote the floral traits, outcrossing rates, and seed production in hybrid rice. The impact of cyanobacteria (Anabaena Oryza (T2), Nostoc muscorum (T3), and their combination (T4) versus the untreated control (T1) was investigated for two years on the growth, floral, and yield traits of five diverse CMS lines, namely IR69625A (L1), IR58025A (L2), IR70368A (L3), G46A (L4), and K17A(L5). The evaluated CMS lines exhibited significant differences in all measured floral traits (days to heading (DTH), total stigma length (TSL), stigma width (SW), duration of spikelet opening (DSO), spikelet opening angle (SOA)). Additionally, L4 displayed the uppermost total stigma length and stigma width, whereas L1 and L5 recorded the best duration of spikelet opening and spikelet opening angle. Notably, these mentioned CMS lines exhibited the highest plant growth and yield traits, particularly under T4 treatment. Strong positive relationships were distinguished between the duration of the spikelet opening, panicle exertion, panicle weight, seed set, grain yield, total stigma length, spikelet opening angle, stigma width, and number of fertile panicles per hill. Cyanobacteria is a potential promising tool to increase floral traits and seed production in hybrid rice.

Growth Regulators Improve Outcrossing Rate of Diverse Rice Cytoplasmic Male Sterile Lines through Affecting Floral Traits.

Cytoplasmic male sterility (CMS) provides an irreplaceable strategy for commercial exploitation of heterosis and producing high-yielding hybrid rice. The exogenous application of plant growth regulators could improve outcrossing rates of the CMS lines by affecting floral traits and accordingly increase hybrid rice seed production. The present study aimed at exploring the impact of growth regulators such as gibberellic acid (GA3), indole-3-acetic acid (IAA), and naphthalene acetic acid (NAA) on promoting floral traits and outcrossing rates in diverse rice CMS lines and improving hybrid rice seed production. The impact of foliar applications of growth regulators comprising GA3 at 300 g/ha or GA3 at 150 g/ha + IAA at 50 g/ha + NAA at 200 g/ha versus untreated control was investigated on floral, growth, and yield traits of five diverse CMS lines. The exogenously sprayed growth regulators, in particular, the combination of GA3, IAA, and NAA (T3) boosted all studied floral, growth, and yield traits in all tested CMS lines. Moreover, the evaluated CMS lines exhibited significant differences in all measured floral traits. L2, L3, and L1 displayed the uppermost spikelet opening angle, duration of spikelet opening, total stigma length, style length, stigma brush, and stigma width. In addition, these CMS lines exhibited the highest plant growth and yield traits, particularly under T3. Consequently, exogenous application of GA3, IAA, and NAA could be exploited to improve the floral, growth, and yield traits of promising CMS lines such as L2, L3, and L1, hence increasing outcrossing rates and hybrid rice seed production.

Style length and flower morphology of three eggplant (Solanum melongena L.) cultivars from Iran affected by fruit load

A common feature of eggplant is its heterostyly. Long-style flowers bear fruits whereas short style ones fail to do so. Heterostyly is influenced by some factors such as genotype, climatic conditions and fruit load. In this study three eggplant cultivars from Iran were cultivated under greenhouse condition. The influence of presence of fruit (two fruits and four fruits) or absence of that on style length and some other flower morphological was studied in three positions of single, basal and additional. The presence of fruit, specially four fruits reduced style length, stigma width as well as mass of flower, pistil and stigma compared to the control in all times during fruit growth, and after fruit harvest they increased again. Fruit load didn’t affect the number of stamen and stamen length. These effects were observed in all three positons of single, basal and additional flowers of all three cultivars. Generally this study showed that fruit load has decreasing effect on style length and size of flowers forming after fruit setting, which reversed after fruit harvesting.

Sexual, apomictic and mixed populations in Handroanthus ochraceus (Bignoniaceae) polyploid complex

Some tropical Bignoniaceae form sporophytic apomictic polyploid complexes are similar to better studied temperate plants. Handroanthus ochraceus is a widely distributed Neotropical savanna tree with both monoembryonic/self-sterile, and polyembryonic/apomictic and self-fertile populations, but lacking chromosome number and morphological comparative studies. We tested if monoembryonic/non-apomictic and polyembryonic/apomictic populations differed in ploidy and morphological features, as a basis to understand evolution and biogeography of these plants. Chromosome number and embryo number per seed were investigated, and uni- and multivariate analyses of flower and leaf morphology were done for five populations of H. ochraceus. We found two pure monoembryonic diploid (2n = 40), and one pure polyembryonic (62–94% of polyembryonic seeds) tetraploid population (2n = 80). One of the diploid populations presented only one individual with 3.2% polyembryonic seeds and was considered a non-apomictic population. Another population showed predominantly polyembryonic (27–66% of polyembryonic seeds) tetraploid individuals, but one diploid individual with 2% of polyembryonic seeds, and was considered a mixed apomictic and non-apomictic population. Morphological analyses confirmed breeding system clusters, and that stigma width, as well as pollen grain area, was consistently larger in polyembryonic populations. Polyploid plants showed larger cells, as well as larger organs and other distinctive features, which will be useful to identify apomictic populations and to future taxonomic discussions. The species can be considered an agamic complex with apomixis associated with neopolyploidy. This trend is also found in other tropical sporophytic apomictics, contrasting with the usual reports linking diploidy or paleopolyploidy to this kind of apomictics.

New insights into floral morph variation in Passiflora incarnata L. (Passifloraceae) in Tennessee, U.S.A.

Passiflora incarnata is a functionally andromonoecious clonal wildflower, native to the southeastern United States, whose primary pollinator is the carpenter bee, Xylocopa virginica. While recent studies looking at reproductive ecology in P. incarnata have classified flowers as one of two morphs (male or hermaphroditic) based on stylar deflexion, preliminary field studies conducted in Tennessee indicated there were five distinct morphs present (three male, two hermaphroditic), supported by stylar deflexion, floral size, and pistil development. The present study sought to test the hypothesis that five distinct floral morphs are present in P. incarnata by sampling 13 floral characters, and to document variation in nectar constituents, volume, and concentration across the five morphs. Five well-established individual plants were examined at three sites in Cookeville, Tennessee. Two-factor permuted analysis of variance of 13 floral characteristics with floral morph and individual plants as factors suggested that morph:plant interactions explained 6%, individual plant explained 18%, and floral morph explained 36% of variation in floral characteristics. Nectar sampling indicated that all morphs produced nectar comprised exclusively of sucrose. Nectar volume generally increased with floral morph size, while nectar concentration decreased. NMDS analysis indicated that four of the five hypothesized morphs were supported as distinct, with morphs 4a and 4b best classified as submorphs due to substantial overlap. The supported morphs are best distinguished by ovary width, ovary length, style length, and stigma width. These findings support a hypothesis that the morphs result from variation in developmental arrest during floral ontogeny. The ecological implications of the morphs and nectar variation are considered for X. virginica with suggestions for additional studies.

Morfologi Bunga dan Korelasinya terhadap Kemampuan Menyerbuk Silang Galur Mandul Jantan Padi

Good male sterile lines should have high and stable sterility, as well as have good characters of flowers that enhances the outcrossing ability. Research was conducted at Sukamandi field station during DS of 2010 to study the character and flowering behaviour and their genetic variability among the new CMS lines. Five new CMS lines were tested in the field in three replicates of randomized complete block design. The results showed that CMS derived from the Wild Abortive, Kalinga and Gambiaca all were early flowering. The new CMS lines have better flower characters than that of IR58025A, including the following: bigger stigma, higher stigma exsertion percentage, wider degree of glume opening, and longer duration of glume opening. Better flowering behaviour enhanced the ability of outcrossing, and resulted in seed set obtained from CMS lines, up to 25.90%; the traditional IR58025A CMS line produced seed set of only 2.98%. The significant positive correlation was found between seed set with stigma width (r = 0.44*), with stigma exsertion (r = 0.54*); and with degree of glume opening of male sterile lines (r = 0.42*); also with filament length (r = 0.47*) and degree of glume opening of maintainer line (r = 0.57**). Those characters are important for the seed set of CMS lines in the hybrid seed production.

Floral morphology and breeding system in Polygonum hastato-sagittatum Mak. (Polygonaceae)

Distyly has been clearly confirmed in Polygonum hastato-sagittatum Mak, which is dimorphic for the intrinsic features of style height, anther height and a suite of ancillary pollen and stigma polymorphisms. The stigma width of long styled flowers is larger than that of short ones, and L-morph (long) stigmas have longer and less number of papillae than the S-morphs (short). Flowers produced significantly smaller pollen grains, but in greater numbers, in L-morph than in S-morph. In P. hastato-sagittatum, style-morph ratios were associated with population size: larger populations always exhibited 1:1 morph ratios, or were slightly L-biased, whereas smaller populations were often strongly L-biased, and only occasionally S-biased. Populations containing only the L-morph were occasionally found, but populations fixed for the S-morph were not observed. The biased style-morph ratios maybe result from morph-specific differences in assortative mating or artificial disturbance. The study supports the theory that evolution of heterostyly reduces the conflict that can occur in sexually monomorphic animal-pollinated species, achieving efficient cross-pollination but simultaneously avoiding self-interference between female and male sexual organs.

Diversity and evolution of the gynoecium in Cuscuta (dodders, Convolvulaceae) in relation to their reproductive biology: two styles are better than one

The gynoecium of 122 species and 14 varieties of Cuscuta (dodders) was investigated by light and scanning electron microscopy to assess its diversity and evolution and to provide a morphological foundation for understanding the different reproductive strategies encountered in the genus. Data were optimized into a consensus tree constructed from three large-scale molecular phylogenies of the genus based on nuclear ITS and plastid trnL-F sequences. The number of styles combined with the stigma shape are the only floral/fruit characters that enable the separation of Cuscuta subgenera. In addition, gynoecium morphology is useful for delimiting species in some clades. The one-style gynoecium of subg. Monogynella is mostly likely ancestral whereas gynoecia with two styles are derived in subgenera Cuscuta and Grammica. Gynoecia with two styles encountered in the latter subgenera provide a greater morphological complexity and flexibility for various reproductive strategies. In subg. Cuscuta, both the equal styles and stigmas continue to elongate and modify their position after the flowers open, until pollination occurs. In subg. Grammica, the two unequal styles may cause a spatial separation of the sexes in the flower, herkogamy, while the two stigmas mature sequentially and have a differential timing of their receptivity for pollen. A nectary consisting of a ring of modified stomata at the base of the ovary, the equivalent of the hypogynous nectary disc present in many Convolvulaceae, was observed for the first time in all Cuscuta species. The vasculature of the styles is reduced, represented mostly by phloem; xylem is present only in subg. Monogynella. Some gynoecial characters, for example papillae diameter, stigma surface area, stigma width, and style width were moderately correlated with pollen volume, pollen polar–equatorial ratio and tectum perforation. Gynoecium features suggest that Cuscuta is allied with the “bifid clade” (Dicranostyloideae) in Convolvulaceae.

Distyly in Polygonum jucundum Meisn. (Polygonaceae)

Distyly has been clearly confirmed in Polygonum jucundum Meisn. The distylous species is dimorphic for tepals, styles, stigmas, and pollen size and number. Long (L)-morph flowers are slightly larger than short (S)-morph flowers. The stigma width of thrum flowers is larger than that of pin flowers, and pin stigmas have longer and fewer papillae than the thrum ones. Flowers of the L-morph produced significantly smaller pollen grains in greater numbers than flowers of the S-morph. We found that Polygonum jucundum is not an obligate cross-pollination plant, and a reliable pollinator of the species is often available in the field. Our study revealed that flower flies are the most effective pollinators of Polygonum jucundum, whereas ants and thrips probably behave as “nectar thieves”; during the foraging process, however, thrips may effect pollination. In addition, other insects visited Polygonum jucundum flowers. The study supports the model proposed by Barrett that heterostyly is a strategy evolved to reduce sexual interference and inhibit self fertilization.

FLORAL MORPHOMETRIC DIVERSITY OF TUNISIAN APRICOT (PRUNUS ARMENIACA L.) CULTIVARS

Thirteen floral morphological characteristics (floral button length and width, corolla width, stigma position and width, petal number, shape, length and width, stamen number, pistil number, length and width) were studied for twelve Tunisian apricot cultivars. Floral buttons (stage D) and flowers at anthesis were used for this study. Average length and width of floral button were 12.53 mm and 8.12 mm, respectively. The average number of petals (05) and average number of pistils (01) were similar for all studied cultivars. A large variability (CV> 20%) was noted particularly for corolla width, stigma width, petal shape and pistil length. These parameters were considered as discriminating characters between the studied cultivars.

The Mallotus Wrayi Complex (Euphorbiaceae)

The Mallotus wrayi King ex Hook.f. complex on the Sunda Shelf of the Malay Archipelago (Malay Peninsula, Sumatra, Java, Borneo) appeared to comprise four species instead of a single, very heterogeneous one. Two synonyms (M. caudatus Merr. and M. lancifolius Hook.f.) are resurrected and a new species, M. spinifructus, is described. Important characters can be found in the density of the hairs (glandular scale-like, simple or stellate), type of stellately bundled hairs, lengths of inflorescences, bracts, and bracts of the terminal bud, and in the stigma width and hairiness.

EFFECT OF TEMPERATURE ON INFLORESCENCE DEVELOPMENT AND FLORAL BIOLOGY OF MANGO (MANGIFERA INDICA L.)

Trees of two mono-embryonic (‘Irwin’ and ‘Sensation’) and two poly-embryonic (‘Nam Dok Mai’ and ‘Kensington’) mango cultivars were exposed to winter temperatures to induce flowering. They were subsequently transferred into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/20°C for 20 weeks. Inflorescence development only occurred on trees that were maintained at 20/10, 25/15 and 30/20°C. Higher temperatures generally increased the inflorescence size while there was an inverse effect on the mean number of flowers per inflorescence with 619.6 at 20/10°C decreasing to 431.3 at 30/20°C. There was an inverse relationship between the length of the anthesis period and temperature. Low temperatures at 20/10°C decreased the percent hermaphrodite flowers in poly-embryonic cultivars but increased the percentages in mono-embryonic cultivars. Style length and stigma width was reduced when the trees were held at 20/10°C compared to those trees held at either 25/15 or 30/20°C. Trees of ‘Kensington’ grown at 20/10°C mainly produced flowers which had short styles (0.62 mm) and small stigmatic surfaces while ‘Nam Dok Mai’ and ‘Irwin’ trees produced some flowers which had deformed ovaries or fused ovaries. A decrease in percent hermaphrodite flowers and floral changes which occur in poly-embryonic cultivars when inflorescences develop under low temperatures (20/10°C), are likely factors contributing to their low fruit set when grown in subtropical climates.

Effect of temperature on inflorescence and floral development in four mango ( Mangifera indica L.) cultivars

To study the effect of low temperature on inflorescence and floral development of mango ( Mangifera indica L.), `Nam Dok Mai', `Kensington', `Irwin' and `Sensation' trees were exposed to natural winter temperatures to induce flowering, and then transferred to controlled-environment glasshouse rooms where day/night temperature regimes of 15/5°, 20/10°, 25/15° and 30/20°C were maintained for 20 weeks. Day/night temperatures of 15/5°C severely inhibited the emergence and elongation of inflorescences of all cultivars with inflorescence development only occurring on trees that were maintained at the warmer temperatures (20/10°, 25/15° and 30/20°C). The time taken for inflorescences to reach maximum length was 15–20 days on trees held at 25/15° or 30/20°C but extended to 54 days on trees kept at 20/10°C. Warmer temperatures generally increased the inflorescence size of all cultivars. At 20/10°C, pollen viability of `Sensation' was significantly lower than the other cultivars, but there was no significant difference between cultivars held at 25/15° and 30/20°C. Low temperatures caused morphological changes in styles, stigmas, ovaries and anther size in all cultivars, and changes were especially pronounced in `Kensington'. Style length and stigma width of all cultivars were reduced when trees were held at 20/10°C compared to trees held at either 25/15° or 30/20°C. Trees of `Kensington' grown at 20/10°C mainly produced flowers that had short styles (0.62 mm) and small stigmas (0.09 mm) while `Nam Dok Mai' and `Irwin' trees produced some flowers with deformed or fused ovaries. Scanning electron microscopic studies indicated that normal `Kensington' flowers had non-symmetrical stigmas that were covered with undeveloped papillae cells. The short-styled `Kensington' flowers (produced at 20/10°C) had a much smaller receptive stigmatic area compared to normal flowers produced at 30/20°C. Low temperature-induced (20/10°C) changes in ovary size in `Nam Dok Mai' and style length in `Kensington' flowers may contribute to low fruit set in these two cultivars when grown in subtropical climates.

Morphological analysis of genetically identified cattails Typha latifolia, Typha angustifolia, and Typha ×glauca

Hybridization between the cattail species Typha latifolia L. and Typha angustifolia L. is frequent throughout northeastern and central North America. While studies are required to elucidate the ecological role of interspecific hybrids, morphological intergradation of the hybrids and parental species limits accurate identification. Although species-specific molecular markers have been developed, some researchers do not have the resources necessary for molecular analysis. Consequently, this study used genetically identified specimens of T. latifolia,T. angustifolia, and their hybrid Typha ×glauca Godr. to discriminate sound taxonomic characters for morphological identification. Leaf width, spike gap, spike width, and spike length were measured for 153 specimens of cattails from Massachusetts, Ontario, Quebec, and Manitoba. In addition, stigma width was measured using a compound microscope. Morphological data were used in discriminant analysis; approximately 90% of the classifications derived by discriminant analysis corresponded to the genetic identity. Discriminant analysis using stigma width, spike length, spike interval and leaf width provided accurate identification for 28 of 31 T. angustifolia specimens, 38 of 41 T. ×glauca specimens, and 20 of 25 T. latifolia specimens. Thus, discriminant analysis of morphological characters can be used to distinguish the hybrid cattail from the parental species with reasonable confidence when molecular resources are not available.Key words: Typha, cattails, discriminant analysis, DNA markers.

Morphological analysis of genetically identified cattails <i>Typha latifolia</i>, <i>Typha angustifolia</i>, and <i>Typha קlauca</i>

Hybridization between the cattail species Typha latifolia L. and Typha angustifolia L. is frequent throughout northeastern and central North America. While studies are required to elucidate the ecological role of interspecific hybrids, morphological intergradation of the hybrids and parental species limits accurate identification. Although species-specific molecular markers have been developed, some researchers do not have the resources necessary for molecular analysis. Consequently, this study used genetically identified specimens of T. latifolia, T. angustifolia, and their hybrid Typha ×glauca Godr. to discriminate sound taxonomic characters for morphological identification. Leaf width, spike gap, spike width, and spike length were measured for 153 specimens of cattails from Massachusetts, Ontario, Quebec, and Manitoba. In addition, stigma width was measured using a compound microscope. Morphological data were used in discriminant analysis; approximately 90% of the classifications derived by discriminant analysis corresponded to the genetic identity. Discriminant analysis using stigma width, spike length, spike interval and leaf width provided accurate identification for 28 of 31 T. angustifolia specimens, 38 of 41 T.× glauca specimens, and 20 of 25 T. latifolia specimens. Thus, discriminant analysis of morphological characters can be used to distinguish the hybrid cattail from the parental species with reasonable confidence when molecular resources are not available.

Genetic and environmental variation in anther, pollen and pistil dimensions in sesame

Measurements of anther (length, width, depth), pollen grain (percent fertility, polar diameter, equatorial diameter, polar diameter/equatorial diameter ratio, volume) and pistil (stigma length, style length, ovary length, total pistil length, stigma width, style width, ovary width) were taken on 12 diverse sesame (Sesamum indicum L.) genotypes on each of four collection dates in 1994. Highly significant differences among genotype means were obtained for all characters except polar diameter. Highly significant differences among environment (collection date) means were found for ten of the 15 characters measured. Highly significant genotype x environment interactions were obtained for all characters except anther length. For the anther characters measured, relatively high repeatability values were found, ranging from 99.8% for length to 87.6% for depth. For the pollen grain characters measured, the repeatability values ranged from 67.6% for percent fertility to 23.1% for polar diameter. For the pistil characters measured, the repeatability values ranged from 94.0% for style width to 49.6% for total pistil length. These results indicate that genotype and environment influence anther, pollen grain and pistil characters. Variation in some of these morphological aspects could influence the consistency and interpretation of male transmission studies on both the applied and evolutionary levels.

Morphological Differences and Changes of the Gynoecium in Short-Lived Flowers of Rosa setigera Michaux and Their Relationship to Dioecy

Rosa setigera is unique within the genus because the plant is cryptically dioecious, the flowers of male and female plants appearing identical. Flowers produce no nectar, and the plants rely upon insects, which feed on or collect pollen, for pollination. The plants' gynoecia in both sexes are extremely similar; however, overall the synstigmatic length, synstylar length, ovary length, ovule length, and ovule width are greater in flowers of female plants than in flowers of male plants. Only the single stigma width of male plants was found to be greater than that of female plants. Furthermore, ovary volume, ovary width, ovule length, ovule width, and ovule volume in flowers of female plants increase over the period of 4 d of a flower's life (i.e., with petals), whereas in flowers of male plants those characters either decrease or remain relatively constant over the 4-d time period. No overall differences in synstigmatic width, synstylar width, single stigma length, synstigmatic area, and ovary width were found. The results indicate that dioecy may be a relatively recent occurrence in this species.

Floral Variation and Distyly in Guettarda scabra (Rubiaceae)

Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma-anther separation is bimodally distributed and can be used to identify a long-styled and a short-styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self-compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short-styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long-styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short-styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.

FLORAL VARIATION AND DISTYLY IN GUETTARDA SCABRA (RUBIACEAE)

Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma‐anther separation is bimodally distributed and can be used to identify a long‐styled and a short‐styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self‐compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short‐styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long‐styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short‐styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.