Saturday, August 26, 2017

Ever Wondered about the Sex Life of Holly?

Ever wondered about the sex life of holly? Well, I have, and let's just say it is complicated! What I am referring to is the genus Ilex, specifically landscape selections of Ilex. Now I know I usually talk about native plants, but this is a topic that is confusing and attractive to delve into, and delve we must! Let's look at several landscape hollies: Red Hollies, Nellie R. Stevens Holly, and Mary Nell Holly.

Naturally Ilex species are dioecious. Dioecious means "two houses" in Latin to reflect the fact that Ilex has male or female flowers on separate plants. Only about 10% of plant species have this condition. Most plants have "perfect" flowers, or male and female parts on each flower. For the benefit of future generations of plants being more fit for their changing environment, plants usually have various mechanisms in place to avoid self-pollination. Dioecy is just one such manifestation. The number of variations on this theme are amazing and clever. Mother Nature is the master at improvisation! Look at the two photos below. The first one is of a female flower. These are easy to distinguish from the berry-like protuberance in the center of the flower. Male flowers lack this structure and have pollen-bearing anthers. The male flowers are so numerous and carry such a large pollen load, that blooming hollies are irresistible to bees. To get berries on your hollies, you must have a male holly that blooms at the same time as the females. As long as there is a male somewhere in the vicinity, bees will locate it and pollinate your female hollies. Bees are amazing!

Ilex female flowers                                                                                                                                                    Wikipedia
   
Ilex male flowers                                                                                                                                                      Wikipedia

Plant breeders have managed to cross several species to achieve various goals, such as greater cold tolerance, and fruit set. Some crosses resulted in female plants that can set fruit without a male holly. These crosses usually contain some Ilex cornuta, or Chinese Holly, since Chinese Holly exhibits a condition called parthenocarpy. Parthenocarpy is the ability of a female plant to form sterile fruit in the absence of a male. Several plants can do this. The trait of parthenocarpy was used to breed "seedless" citrus and other plants. 
To complicate matters, Ilex cornuta, and its hybrids, sometimes have perfect flowers on male plants, followed by red fruits. These fruits contain four apparently normal-looking carpels, which may-or-may-not be viable. 

And then it becomes complicated! There is a group of hollies bred for size and color, referred to as "Red Hollies." They were developed by Mitch Magee's Evergreen Nursery in Poplarville, Mississippi. The name comes from the red tint on new growth. These are upright attractive plants with a strong pyramidal growth habit. This group includes Ilex 'Festive", Ilex 'Cardinal', Ilex 'Oak Leaf', Ilex 'Little Red', and Ilex 'Robin'. 'Oak Leaf' Red Holly has a confusing and complex breeding history. I was curious if parthenocarpy or plant sex through pollination was working to form berries. In an effort to understand the formation of fruit on the Oak Leaf Red Holly, I emailed several holly experts, and did some research. 'Oak Leaf' Red Holly has functional male and female flower parts, perfect flowers, so it can pollinate itself, so no parthenocarpy, just fertilization. The parent is an open-pollinated Mary Nell holly. Mary Nell is a three-way hybrid. Oak Leaf has an unknown male parent. Unlike normal dioecious hollies,‘Oak Leaf’ is not female but a hermaphrodite.


The Red Hollies, as a group, are a perplexing bunch of hybrids.  All are claimed to be open-pollinated seedlings of 'Mary Nell', which is itself the result of controlled hybridization and is Ilex (cornuta 'Burfordii' × pernyi) 'Red Delight' × latifolia). You can imagine all of the male pollen flying around at a holly propagation grounds, and that is why the identity of the male pollinizer remains a mystery. Oakleaf holly ('Conaf') and its branch sport Oakland ('Magland') are variously listed on gardening websites as male, female, and both. The US Plant Patents on these cultivars says the flowers are "perfect", meaning having functional male and female parts.  These plants do not have female flowers, as are present in most familiar hollies, (i.e. lacking a visible pistil), nor do they have male flowers (which lack functional pollen-bearing anthers).  Rather, their flowers have small pistils surrounded by four pollen-bearing anthers.  Botanically speaking, these would be considered androgynous, or hermaphroditic.

There is another Oak Leaf holly, Ilex 'Festive" ('Conaf'), which displays a different twist on plant sexuality.  This plant appears to be andromonecious, that is, bearing both traditional male flowers, as well as occasional perfect flowers.  It does not, however, seem to bear any female flowers.  In each blooming season, the vast majority of the flowers are male, and appear to have moderate amounts of pollen.  The perfect flowers tend to appear at the end of the blooming cycle, and produce misshapen, red fruits. 



As for male pollenizers for Oakleaf holly, it seems that this plant does not produce a lot of fruit because of its complicated genetics. I communicated with Dr. James Resch, Ilex specialist, and he says even in nursery settings, where pollen from many species and hybrids is available, Oakleaf holly never seems to develop numerous fruits. It may be that the plant's complicated pedigree has created so many chromosomal mismatches, with would-be pollenizers, that effective pollination can only rarely happen.
Ilex aquifolium                                                                                                                                                       Wikipedia

Two other super popular hollies are also the result of genetic crosses. They are gorgeous with their pyramidal habit, large and glossy foliage, and, of course, the beautiful berries. Both Ilex 'Mary Nell' and 'Nellie R. Stevens' have anthers that do not produce pollen, meaning that they do not have functional male flower parts. These two plants produce fruit through parthenocarpy and by being pollinated by a male I. cornuta or I. pernyi. A male selection suggested as a pollenizer is 'Edward J. Stevens'. 'Nellie R. Stevens' is the result of a cross between Ilex cornuta and Ilex aquifolium. Normally, Ilex aquifolium does not grow well in the heat and humidity of the South, but with the addition of Ilex cornuta genes, 'Nellie R. Stevens' is a long-standing staple in Southern gardens. 'Mary Nell' is a three-way cross with Ilex cornuta, Ilex pernyii, and Ilex latifolia. It is still helpful to have a male holly that blooms at the same time to increase fruit set. It is thought the almost ANY male holly that blooms at the same time will work, but I do not know this as a fact. 
Nellie R. Stevens Hollie                                                                                                                             John Paul Endicott

How to Have a Bee Friendly Garden

Nothing excites me more than to see wildlife in my garden attracted by the plants I bring in, and the wildlife-safe organic gardening practices I follow. This week at the Master Gardener Conference, Dr. Gordon Frankie, the highly respected professor and entomologist, gave us research-based tips on how to maximize native bees in the garden.  

My pollinator garden                                                                                         S. Reeve          


Native bee diversity is promoted by providing at least twenty different blooming plants. Different species of native bees will be attracted by different plants. When you maximize choice, you automatically increase your chances of attracting a wide variety of native bees. Of the estimated 3,600 species of bees in the United States, California is home to about 1,600 species of bees. You may have never noticed many bees before, but once you become interested in seeing bees in the garden, you start to develop “bee eyes” and you will see them everywhere. 

Many native bees are very small and very fast, and you may think they are flies, but some, like the Carpenter bee (Xylocopa varipuncta), are easily recognizable, about an inch long, and so entertaining to watch. Good plants to attact Carpenter bees are Leucophyllum frutescens, Senna  and Wisteria selections, and Caesalpinia mexicana. Wisteria flowers, in particular, have large flowers that only a large bee can open. Interestingly, Xylocopa varipuncta, is a sexually dimorphic species, and the males and females do not look at all alike. Males are often called, “teddy bear” bees because of their furry brown bodies. While females are shiny black with a violet cast. Males set up nesting territories that they patrol, looking for unmated females.  Using glands in their thorax, males release a scent that perfumes their territories. Females chose mates based on the quality of the fragrance. Unlike most bees that only live a matter of weeks, female Carpenter bees can live for several years.
Xylocopa varipuncta female on Caesalpinia mexicana                                                                                            S. Reeve
Once you develop “bee eyes” you will start to see the differences in the small flying insects, and you will recognize that bees look different than flies, and even wasps. Important differences include the fact, that bees generally have hairy or furry bodies, while wasps and flies do not.  Female bees also carry pollen on various locations on their bodies. The fur on their bodies makes it easier to do this. Bees and wasps, like other members of the Hymenoptera, have a narrow constriction in their midsection. Hence the term, “wasp waist.”  Flies do not have this. Bees and wasps also have two pair of wings, compared to only one pair for flies.  There are some flies that are excellent bee mimics, they even have the striped furry bodies, but the number of wings and lack of a mid-section joint gives them away. 

Bombus vosnesenskii gathering pollen from California poppy                                                                            S. Reeve

Besides, the wonderful bounty of life your bee garden will attract, bringing in bees will help you with your vegetable garden. Native bees are terrific pollinators. Be sure an include Lavendula ‘Provence’, a particularly enticing selection for bees, in your vegetable garden to bring in more pollinators. Let herbs and vegetables go to flower to attract even more bees. Kale, cilantro, basil and others will be covered in bees if allowed to flower.  If you are an early riser, go look at your squash blossoms, and you will certainly see the medium-sized Squash Bee (Peponapis pruinosa) deep in the squash flower. 
Peponapis pruinosa in squash blossom                                                                                                                    S. Reeve

To attract the most bee diversity,  plan your garden in the sunniest area, and include plants that have a continuous succession of bloom from February through October. In California we are lucky to have bees in the garden for most of the year.  Having flowers for most of the year, will insure a good food source for the many species of bees that nest all through the year, and often, multiple times during the year. Bees are natural searchers, and will soon find what you have planted. Experiments show, that even in the most urban gardens, bee diversity can increase dramatically if flowering plants are added. Plants in the Asteraceae, Lamiaceae, Rosaceae, Polygonaceae, Malvaceae, and Papaveraceae are particularly attractive for bees. Bees gather pollen and nectar, but not necessarily in the same plant. Pollen is used to provision the nest as food for bee larvae, and nectar is a food source for adult bees. A broad assortment of flowering plants will provide something for many different species.  Plant in large patches of at least 2 square meters, so bees can easily locate the flowers. Flowers in blues, whites, and yellows attract the most bees. 
Bombus melanopygus on Echium fastuosum                                                                                                           S. Reeve

While native plants are certainly important for feeding and nesting bees, non-natives fill an important role, as they bloom in the summer, when many natives are dormant. Some of the best bee plants are: Echium, Arctostaphylos, Phacelia tanacetifolia, Nepeta, Caryopteris, California poppies, Cosmos bipinattus, Ceanothus, Encelia, Gaillardia, and Calandrinia. Be sure to garden without pesticides, particularly neonicotinoids, to keep your bees safe.