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The genus Coreospsis is Florida’s state wildflower. One species, Coreopsis leavenworthii, is nearly endemic to Florida and is highly desirable for use in highway beautification. Maintaining genetic integrity is critical for C. leavenworthii producers, growers, and users. Coreopsis tinctoria is closely related to and shares similar habitats with C. leavenworthii in Florida. Previous studies indicated that the two species could hybridize and the F₁ hybrids showed chromosomal aberrations and reduced pollen stainability. There has been strong concern that pollen-mediated gene flow from C. tinctoria could contaminate the gene pool and compromise the genetic integrity of C. leavenworthii. In the current study, hand pollination showed that C. leavenworthii and C. tinctoria were highly compatible. F₁ hybrids were fertile and readily produced F₂ and BC₁ individuals. Inheritance studies indicated that the maroon spot on the ray flower is controlled by a single dominant allele and is homozygous in C. tinctoria. This spot serves as a reliable, easy-to-score morphological marker to detect pollen-mediated gene flow from C. tinctoria to C. leavenworthii. Following a discontinuous design, gene flow studies were conducted under field conditions in central Florida over 2 years. The highest rate of pollen-mediated gene flow from C. tinctoria to C. leavenworthii was 4.2% and occurred when the two species were grown 1.5 m apart. Gene flow from C. tinctoria to C. leavenworthii under field conditions followed a leptokurtic curve. Based on the obtained regression equation, separating the two species by 60 m or more could lower the pollen-mediated gene flow from C. tinctoria to minimal levels and protect the genetic integrity of C. leavenworthii.

Lantana camara, a member of the verbena family, is a popular ornamental yet highly invasive plant. It can escape from cultivation through seed dispersal and can contaminate native lantana species (Lantana depressa) through cross-pollination. Ploidy manipulation is being used as a genetic approach to produce sterile, noninvasive lantana cultivars. Polyploids have been observed in lantana (Lantana), but little information is available about the mechanisms for lantana polyploidization and the possible effects of natural polyploidization on the sterility (or fertility) of lantana triploids. In this study, we analyzed the ploidy level of more than 1500 lantana progeny from self, open, and/or controlled pollinations of 10 commercial cultivars and seven breeding lines. Our results confirmed the occurrence of unreduced gametes, specifically, unreduced female gametes (UFGs), in lantana. The frequency of UFG formation varied among commercial cultivars, and cultivars/breeding lines could be categorized into two groups: UFG producers and nonproducers. Tetraploid cultivars Gold, Pink Caprice, and Radiation fall into the UFG-producing group, while diploid cultivars Cream, Denholm White and Lola and tetraploid cultivars Carlos, Dallas Red and Irene belong to the nonproducer group. The frequency of UFG formation observed in nine UFG producers was 5.5% to 100%, varying with cultivar, growing condition, and/or pollination scheme. Progeny of the cross between ‘Carlos’ (seed parent) and ‘Gold’ (pollen parent) also showed the ability to produce UFGs, indicating that the trait (UFG formation) could be transmitted from ‘Gold’ to its progeny and is likely to be controlled by nuclear gene(s). Lantana triploids with or without the UFG-forming ability in its genetic background showed a significant difference in seed set: the former produced abundant seed when pollinated, while the latter produced little or no seed. The results stress the need to avoid using lantana with UFG-forming ability as parents in crosses designed to produce sterile triploids for invasiveness control. Additionally, the results from this study suggest multiple pathways for emergence and evolution of polyploids in cultivated and naturalized lantana populations.

Lantana camara is an important plant for the environmental horticultural industry, yet it can be invasive, cross-pollinating with native lantana and dispersing fruit (and seeds) to natural and agricultural lands. Identification and development of sterile cultivars is much needed to meet industry and consumer needs for noninvasive plant materials. Previously we evaluated the male fertility of 32 L. camara cultivars/breeding lines at five ploidy levels. This study was to assess their female fertility and understand the relationship between female fertility and ploidy level and the production of unreduced female gametes (UFGs) in L. camara. These cultivars/breeding lines significantly varied in percent fruiting plants (6.3% to 100.0%), percent fruiting peduncles (0.3% to 98.8%), fruit per peduncle (0.003 to 7.173), seed germination (0% to 57.1%), and female fertility index (0.003 to 2.998). Certain diploids (e.g., ‘Denholm White’) were highly female-sterile. Eleven of the 13 triploids evaluated were UFG-producing and rather fertile. The two non-UFG-producing triploids had the female fertility index of 0.005, thus most sterile. Tetraploids, especially those producing UFGs, were prolific fruit producers. These results show that ploidy level and UFG production play a significant role in determining fruit (seed) production capacity and female fertility of L. camara. None of the commercial triploid cultivars evaluated reached desirable levels of male and female sterility, indicating a strong need to develop new lantana cultivars that are male- and female-sterile. Our results suggest that production and selection of triploids can be effective to sterilize L. camara, but it is imperative to select diploids and tetraploids that do not produce UFGs as the breeding parents.

The genus Caladium Vent. is a member of the family Araceae; some of its species are cultivated as ornamentals. The present study was conducted to determine the genome size, somatic chromosome number, and their variation within 63 accessions representing 10 species of Caladium. Caladium genome sizes estimated using propidium iodide staining and flow cytometry ranged from 2.98 pg/2C in Caladium lindenii Engl. to 9.89 pg/2C in Caladium ×hortulanum Birdsey ‘Chang Suek’. Two genome size groups (large and small) were evident among the 63 caladium accessions. The average genome size of 36 caladium accessions in the large genome size group was 9.29 pg/2C, roughly twice that of the 27 accessions in the small genome size group (4.50 pg/2C). Microscopic examination of squashed root tip cells revealed seven somatic chromosome numbers among 39 caladium accessions, including 2n = 18, 20, 24, 26, 30, 34, and 38, and provided the first chromosome counts for four caladium species new to Caladium. The results support the species status of C. marmoratum Mathieu ex K. Koch, C. picturatum K. Koch & C.D. Bouché, and C. steudneriifolium Engl. that were merged into C. bicolor (Aiton) Vent. previously and also support the species status of C. clavatum Hett., Bogner & J. Boos, and C. praetermissum Bogner & Hett., two species recently established in or transferred to Caladium. The results suggest that C. bicolor and C. schomburgkii Schott, not C. picturatum or C. marmoratum, are the chief parents of the fancy-leaved caladium (C. ×hortulanum). Four caladium cytotype groups (CCG-1 to -4) were identified in scatterplot of chromosome number vs. genome size. The genome size of C. bicolor, C. schomburgkii, and C. ×hortulanum in the CCG-4 is approximately twice that of C. humboldtii (Raf.) Schott and C. picturatum in the CCG-2, and the chromosome number of C. clavatum and C. marmoratum in the CCG-3 is close to twice that of C. humboldtii and C. picturatum in the CCG-2, both suggesting possible genome duplication or tetraploidization events in Caladium. However, the chromosome number of the CCG-4 species does not correspond to an expected 2n = 36 or 40, and the genome size of the CCG-3 species does not correspond to an expected 8.98 pg/2C. Conflicts between genome size and chromosome number indicate that genome duplication events were likely followed by chromosome fusions/losses in the formation of CCG-4 species and DNA losses likely followed tetraploidization in the formation of the CCG-3 species. The high level of cytological diversity found within Caladium affects germplasm collection and preservation efforts as well as breeding programs in the genus.

Lantana species are an important component of the U.S. environmental horticulture industry. The most commonly produced and used species are L. camara and, on a smaller scale, L. montevidensis. Both were introduced to the United States from Central and/or South America. Lantana species native to the continental United States include L. canescens, L. depressa, L. involucrata, etc. and most of them have not been well exploited. This study was conducted to obtain information about somatic chromosome numbers, karyotypes, and genome size of these five species. Nuclear DNA content in these species ranged from 2.74 pg/2C (L. involucrata) to 6.29 pg/2C (L. depressa var. depressa). Four chromosome numbers were observed: 2n = 2x = 22 in L. camara ‘Lola’ and ‘Denholm White’, 2n = 4x = 44 in L. depressa var. depressa, 2n = 2x = 24 in L. canescens and L. involucrata, and 2n = 3x = 36 in L. montevidensis. Two basic chromosome numbers were observed: x = 11 in L. camara and L. depressa var. depressa, and x = 12 in L. canescens, L. involucrata, and L. montevidensis. Analysis of somatic metaphases resulted in formulas of 20m + 2sm for L. camara ‘Lola’ and ‘Denholm White’, 12m + 12sm for L. canescens, 44m for L. depressa var. depressa, 10m + 14sm for L. involucrata, and 32m + 4sm for L. montevidensis. Satellites were identified in all five species, but were associated with a different chromosome group in different species. L. depressa var. depressa had the longest total chromatin length (146.78 µm) with a range of 1.88 to 4.41 µm for individual chromosomes. The maximum arm ratio was observed in L. canescens, with a ratio of 2.5 in chromosome group 3. L. depressa var. depressa was the only species that had all of its centromeres located in the median region of the chromosome. The results show significant differences in nuclear DNA content, chromosome number, and karyotype among three native and two introduced lantana species and will help to identify, preserve, protect, and use native lantana species. The information will be helpful in assessing the ploidy levels in the genus by flow cytometry.