| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 505 July 1, 2016 | aceska@telus.net | Victoria, B.C. |
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One of the earliest blooming wild flowers in the Okanagan, typically flowering in March and April but occasionally as early as late January, Ranunculus glaberrimus generally bear 5 petals (Photo 1). The number of petals, however, varies widely as does their size and shape. The highly reflective, bright yellow petals are concave and may direct sunlight onto the reproductive organs as well as possibly providing warmth to attract insects for pollination.
The earliest flowering plants typically have 5 petals but the number of plants with more than 5 petals appears to increase as the season and temperature advances. Martin has observed late-flowering plants with more than 20 small-sized petals in the Vernon area, and Scotter noted 13 petals on plants in the Kelowna area (Photo 2). Martin and Scotter have also observed apetalous patches of Ranunculus glaberrimus mixed with apparently normal plants. The flowers without petals appear to be setting seed in sufficient quantity to extend the patches, suggesting that these plants may be self-pollinating.
Apetalous populations have been found at five locations in the Okanagan (Photos 3 and 4). Martin has made observations on lower grassland slopes on the south side of Vernon Hill above Buchanan Road (50° 14' N, 119° 12' W, 540 m) over a period of several years. Scotter has made observations over the flowering season of the plant on the eastern outskirts of Kelowna over a period of six years (49° 53' N, 119° 20' W, 610 m). Other apetalous populations were found near the summit of the trail to Rose Valley (49° 53' N, 119° 33' W, 730 m), Quail Ridge Linear Park (49° 56'36" N, 119° 24' W, 475m), and on Knox Mountain (49° 54.759' N, 119° 29.461' W, 400 m). An extensive search would likely reveal many more of the apetalous type. Scotter and other members of the Central Okanagan Naturalist Club found it on Land Conservancy property on the east side of the Similkameen River, a few metres north of the International boundary adjacent to Washington State (49° 00' N, 119° 42' W, 280 m) on 30 April 2013.
Herbarium vouchers of the petaled type (collection number KEL001) and the apetalous type (collection number KEL002) are deposited at the University of British Columbia Herbarium, Vancouver. Both collections are from the eastern outskirts of Kelowna near Highway 33. The specimens were marked on 1 March 2015 and observed weekly until they were collected on 31 March.
It has been suggested that the lack of petals could possibly be caused by high wind, rain drops, natural petal drop as flowers age, or by foraging insects, birds, and mammals. To address those possible causes, Scotter collected 10 stems each of the apetalous and petaled forms at three different locations. The plants chosen had one flower open and one or more buds. Those plants were placed in water and taken to a greenhouse-like structure without insects, birds, mammals, wind, or rain. Stems that produced an additional flower or flowers were true to the type; the petaled type produced petals and the apetalous buds opened but did not produce petals. Observations in 2015 at the eastern Kelowna site started on 1 March. Both types were just initiating flowering, which is well before any natural petal drop would be expected. Except for early in the flowering season any of the factors, or a combination of those factors, could result in plants being without petals. Therefore, critical examination is required to determine if plants were apetalous throughout the flowering season.
The apetalous type of Ranunculus glaberrimus is not mentioned by Hitchcock et al. (1964), Moss (1983), Whittemore (1997), or Douglas et al. (1999). Brayshaw (1989) does mention that petals may sometimes be absent but without additional discussion.
It is notable that the species account for Ranunculus glaberrimus in the Flora of North America (Whittemore 1997) makes no mention of plants lacking petals, and the only comment found during an internet search was a rather ambiguous reference to a population of plants discovered in Colorado that were presumed to have lost their petals by some physical cause.
Extending the search beyond the subject species produced references indicating examples of other species in this genus occasionally having been found without petals. Fisher et al. (1979) collected and transplanted two sympatric species (Ranunculus eschscholtzii and R. suksdorfii), from 75 localities in western North America for study under experimental conditions. They reported an anomalous condition of apetaly in R. eschscholtzii in some high rainfall sections of the western Cascade Mountains of Washington. There the hexaploid population of R. eschscholtzii mixed with the diploid population of R. suksdorfii, and the apetalous state replaced the normal form because of competition for pollinators and hybrid sterility. Some apetalous variants were observed in most populations of R. eschscholtzii that they examined. They also reported an apetalous population of R. eschscholtzii outside the range of R. suksdorfii at Mt. Arrowsmith on Vancouver Island. However, that would seem to weaken their argument of cross-specific pollination as a cause of apetaly.
Apart from emphasizing the propensity for apetaly to occur throughout the genus Ranunculus, the study by Fisher et al. (1979) does not explain the condition we are describing. Those authors conclude an effect from the possible transference of pollen between R. eschscholtzii and R. suksdorfii. In our case no other Ranunculus species flowers concurrently with R. glaberrimus. Those that could reasonably be expected to occur within the same general geographical region typically occur in habitats other than the dry grassland of R. glaberrimus. Moreover, none of these are taxonomically allocated to the subgenus Epirotes in which R. glaberrimus belongs.
As we have observed Ranunculus glaberrimus in the Okanagan, several questions emerged that need to be addressed with detailed study requiring greenhouse facilities, laboratories, and expertise in a multitude of fields. The comments and questions that follow are provided to stimulate future research on this interesting native plant.
1. The presence of apetalous plants is so obvious in some parts of British Columbia, particularly the Okanagan that it is difficult to imagine previous generations of botanists and naturalists missed reporting them. Question - Is the apetalous plant a recent phenomenon; when were the first reports or voucher specimens; are reports now becoming more frequent?
2. For a character to be conserved and increase in frequency it should have evident advantages over petalous plants. Question - Is the apetalous character increasing; do apetalous plants continue to flower without petals; is the phenomenon regionally restricted; where it occurs are petaled plants eventually eliminated or do they convert or neither?
3. When Ranunculus glaberrimus flowering is initiating, in the late winter, pollinator availability may be limited. Question - How do numbers of visiting insects compare between the two flower types; how do the two types become pollinated and/or set seed; are there reasons to expect wind pollination; are there reasons to presume self-pollination by movement of anthers at certain times to transfer pollen to stigmas?
4. If there are physiological differences giving one type an advantage over the other it should be possible to draw some conclusions. Question - Are there habitat differences identifiable between petaled and apetalous plants in timing of functions; start of pollen production; length of time pollen produced; number of anthers; number of seeds; size of seeds; fertility of seeds?
5. "Normal" Ranunculus flowers carry nectaries near the base of petals, presumably an inducement to attract potential pollinators. Question - Do petaled flowers actually produce nectar and can insects be seen to utilize it; what insects visit petaled flowers; is nectar sufficiently costly to the plant to give apetalous forms an advantage?
6. Without nectaries apetalous flowers presumably are unable to attract insects. Question - Can insects be seen visiting apetalous flowers; in the absence of nectaries is nectar available at other locations among the fruiting organs?
7. The highly reflective interior surface of petals as well as their early concave shape has been advanced as possible adaptions to concentrate sun rays to provide warmth to (a) speed maturity of fruiting organs under cool early spring conditions and (b) attract potential pollinators by offering warm and protected conditions within the flower. Question - Do petaled plants actually obtain any advantages in this?
8. So far as known, cross-breeding experiments have not been carried out between petaled and apetalous plants. Question - Is there a consistent genetic response to cross-breeding indicating one type to be dominant and the other recessive; are there differing results from pollinating petaled plants with apetalous plant pollen and apetalous plants with petaled plant pollen?
9. Climate changes may have unexpected and unrealized effects. In British Columbia wetter winters, longer cool springs and hotter, drier summers have been offered as possible factors of change. Higher average annual temperature and length of sun exposure may be more effective on south-facing, low-elevation, heat-prone situations. Question - Is there a difference in numbers between petaled and apetalous plants in 'hot' locations compared with 'cool' (i.e., higher and north-facing) locations?
10. Although not obviously connected with the presence of plants producing petaled and apetalous flowers, Ranunculus glaberrimus has attracted comment for often bearing flowers with anomalous petal numbers. When this occurs it appears that the initial flush is of "normal" 5-petaled flowers while those developing later as temperatures rise may show irregular numbers of narrower, and flattened petals ( as opposed to being concavely curved). Question - Can the propensity to produce numerous petals be linked in any way with petaled and apetalous plants; over time does production of narrower petals eventually lead to abandonment of developing petals; do narrow petals still carry nectaries?
11. As the above ground parts of the fruiting plants senesce they wilt and the seed heads end up on the ground around the parent plant and therefore should germinate close to it. Mature plants, however, are more or less well separated and not surrounded by new individuals. It would not be easy for the seed heads to roll or be blown away through the surrounding vegetation. Question - Do ants collect dropped seeds and disperse (myrmecochory) them; do seeds have tasty bodies to attract other insects?
12. Ranunculus glaberrimus populations support heritable variation with respect to petal size and number and allocation to male and female structures. Question - What is maintaining this variety in the population; is the apetalous type merely a consequence of genetic recombination producing slightly less fit individuals in a variable population? The Quail Ridge Linear Park site, near the University of British Columbia Kelowna campus, is in an open Ponderosa Pine (Pinus ponderosa) / grassland forest. It is the largest of the sites mentioned above and has the largest population of apetalous plants. An estimated 2 to 3 percent of the R. glaberrimus are apetalous. The site is easily accessible and may be ideally suited for future research.
Photo 1. (Left) Typical flowers of Ranunculus glaberrimus with five or six bright, shiny yellow petals that are slightly concave. Photo: John Theberge. Photo 2. (Right) Ranunculus glaberrimus with 13 petals which are smaller than those with only 5 petals. Plants that flower later in the season are more likely to have additional petals. Photo: Sarah Heselgrave. Photo 3. (Left) Apetalous Ranunculus glaberrimus at the eastern outskirts of Kelowna near Highway 33. Photo: Peter Green. Photo 4. (Right) Apetalous Ranunculus glaberrimus along the Rose Valley trail near West Kelowna. Photo: Jorma Jyrkkanen.
Few weeks ago I was surprised when I received a lavishly illustrated compendium on the temperate species of butterworts, Pinguicula of the Temperate North. It took me a while before I remembered that I supplied one of my photos of Pinguicula villosa leaves to this publication and that this volume was meant as a gift in return for the photo. Pinguicula of the Temperate North is the first volume of a series of "two books that document all carnivorous butterworts (Pinguicula) of the world, for the very first time and in unparalleled detail." This compendium is a bibliographic nightmare. Each of its two volumes has an individual title, but the pagination continues from the Volume 1 to the Volume 2. Bibliography of all the cited references is in the second volume, together with Appendices, Glossary and Index to both volumes. In addition, The section on botanical illustration that is meant as a preface to the Volume 2, is published at the end of the Volume 1. In short, you have to buy both two volumes if you want to have a Conclusion, Bibliography and the Index to both volumes.
VOLUME 1: Pinguicula of the Temperate North
ISBN: 978-1-908787-14-9
Pages: 360
Images: 329
Page size: 270 x 205 mm
Cover: hardcover with dust jacket
Contents:
VOLUME 2: Pinguicula of Latin America
ISBN: 978-1-908787-15-6
Pages: 368
Images: 394
Page size: 270 x 205 mm
Cover: hardcover with dust jacket
Contents:
The compendium was published by the Redfern Natural History Productions, Poole, Dorset, England. For ordering information see http://www.redfernnaturalhistory.com/
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