Bulbs and Corms

This post and the previous one are based on an article from the Fall 2007 issue of Fremontia: Journal of the California Native Plant Society. That issue was a special edition on chaparral. The article I'm focusing on this time is "Chaparral Geophytes: Fire and Flowers" by Claudia Tyler and Mark I. Borchert.

Geophytes are plants that grow from a bulb or corm. I will refer to all of them as "bulbs" for simplicity. California has lots of great geophytes that are wonderful to see in the wild and also beautiful garden plants. Geophytes can be found in several habitats including grasslands, coastal sage scrub and chaparral. The Fremontia article addressed what happens to geophytes in chaparral before and after a fire.

Inflorescence of  Chlorogalum pomeridianum in my garden. Its common name, Soap Plant, comes from the fact that Native Americans used the bulb to make a version of soap

The authors of the article did their study in the mountains of Ventura and Santa Barbara Counties. They studied two species, Toxicoscordion (formerly Zigadenus) fremontii, commonly known as Fremont's Star Lily, and Chlorogalum pomeridium (Soap Plant). I believe their findings may also apply, at least in part, to other geophyte genera including Bloomeria, Brodiaea, Calochortus, Dichelostemma, Hesperocallis, Triteleia, and others.

Their first finding was that flowering and seed production are almost completely limited to the first year after a fire. And they don't just make a flower or two. They produce an extravagant display. It appears that the trigger for flowering is the increased light that the geophytes receive once the larger shrubs are removed. It isn't necessarily fire that does the job. Pruning could accomplish the same thing, but fire is the more common cause of shrub removal in the wild. In any case, giving a geophyte a big blast of sunlight results in both dramatic flowering and subsequent seed production.

What happens the next year? The plants shrank after flowering and typically do not flower again for several years. It seems that the energy required to produce a showy display of flowers comes from drawing stored food from the bulb. In so doing, the plant is considerably depleted. It has to rebuild that reserve of food in the bulb by putting out foliage for photosynthesis but no flowers. When geophytes do flower, the ones with the biggest bulbs produce the most flowers and seeds, and it takes time to build up a large bulb.

So geophytes actually need two things to flower: (1) lots of sunlight, and (2) enough energy stored in the bulb. 

Brodiaea filifolia (Thread-leaf Brodiaea) in my garden

The seeds produced after flowering need to germinate during the winter following the bloom. Any seeds that don't germinate will likely be eaten by insects or small mammals. Unlike many other chaparral plants, geophyte seeds don't have much longevity and so don't build up a seed bank in the soil. Seedlings have to get established and start building up a bulb in order to survive. Furthermore, seeds aren't the only things that get eaten. Gophers and some other burrowing animals will eat the bulbs. I think this explains in part why geophytes are not more numerous.

In still later years the chaparral shrub cover once again deprives the geophytes of light. Do they stop growing? No, just the opposite. Geophytes in mature chaparral use whatever light they can get to grow substantially. Without the energy drain of flowering, they can save up a lot of carbohydrates in the bulb, trying to get that bulb as big as possible before it has to bloom again. In really mature chaparral areas it could be 50 years or more between fires, and thus also between blooms.

I have a lot of Dichelostemma capitatum in my garden. I got the original bulbs from a former friend who lived a couple of miles away in Encinitas. His lot had a small section of native slope that had Dichelostemma and non-native grasses. He did not appreciate the beauty of the flowers and he was planning to regrade that slope in order to build something on it. He let me dig up the bulbs first. I got about 100 of them, and I picked out the biggest ones. I didn't know about the relationship between bulb size and flowering, but I couldn't take all the bulbs so I just went for the biggest ones. I set up a dedicated area for them with no competing plants and I planted them densely, the way they were growing previously. I left the soil bare.

Dichelostemma capitatum in my garden several years ago

They did really well in my garden right from the start, with lots of flowering. My guess is that they responded as they would have after a fire. After that, their flower production seemed to decline and at that time I didn't know why. Now, after reading this article I understand that they needed to rebuild their energy reserves. Their relative lack of flowering was counterbalanced by their reproduction. Lots of seedlings came up and many survived. Later, I observed that the larger bulbs were producing bulblets, little baby bulbs. My original 100 has expanded to 200 or more. I dug out some bulbs to get them going in other areas. 

Bulb of Dichelostemma with bulblets

Many years later, an oak tree that I planted nearby got much bigger and now shades the Dichelostemma area all afternoon. They still get some sun, just not all day. I noticed that flower production went down further, but leaf growth ramped way up. The bulbs are now putting out huge, lush, floppy leaves that don't even look like Dichelostemma leaves. When this first started happening I thought the leaf growth was excessive and might be interfering with flowering, so I trimmed off some of the leaf growth. It was like mowing a lush lawn; the leaves grew right back in a couple of weeks. Now I understand (I think) what is going on. As the article suggested, when geophytes are shaded by chaparral shrubs they go into the mode of energy production and storage. In the first couple of years after I planted them in my yard they were experiencing something like the first couple of years after a fire, with abundant sunshine and no competition. Now they are hunkering down, photosynthesizing as much as they can, and storing up food for the day when a fire will trigger them to flower profusely once more.

I have seen a similar dynamic with Brodiaea filifolia. It is not a chaparral species, occurring in either vernal pools or grasslands. But I think it is similar to the other geophytes in that it needs a recovery period after flowering. The production of flowers and seeds takes a lot out of a plant. It needs a few years to get back to where it was before it flowered. So you don't see all the Brodiaea bulbs in a population flowering at the same time. In a given year, a few are flowering while most are in some stage of recovery.

Calochortus species occur in a lot of different habitats including chaparral, and I think the foregoing applies to them as well. I had to buy Calochortus bulbs and they are a bit pricey so I have tended to plant just one or two at a time. This also matches the way I have seen them growing in the wild, not in dense patches but singly mixed with other plants. I have planted Calochortus bulbs that flowered extravagantly the first year. Then I never saw them again for years. I now believe they are still there in the soil, slowly growing, gradually recovering from the toll of their last flowering episode.

Calochortus venustus in flower, Spring 2010. Bloomed again in 2014.

 In an earlier post I described buying some Bloomeria crocea bulbs and planting them in the garden. I bought ten bulbs and planted them in an area where I already had three. They didn't all bloom last year, but several did. I planted a Salvia brandegeei nearby and it is now covering the Bloomeria space. It will be interesting to see if any bloom this coming spring.

 My new approach to geophytes in the garden is to alter my expectations about flowering. I will probably get abundant flowering the first year. After that I should expect several years of few or no flowers while the bulbs recover. If some of my other plants shade out the bulbs, that's not necessarily a problem as it mimics the natural dynamic in chaparral. Eventually, though, the bulbs would like to get full sun exposure again. I can either wait for natural changes in the garden to provide this or I can make it happen by strategic pruning. But I don't need to be in any hurry about this. The longer the interval between flowering episodes, the bigger the bulbs will get so that the next bloom will be even more dramatic.

Manzanita Reproduction

I recently came across Fall 2007 edition of Fremontia, the Journal of the California Native Plant Society. This edition was a special issue devoted to Chaparral. I love Fremontia and I especially love this special edition. There were two articles that particularly impressed me. One dealt with the Manzanitas and Ceanothus (primarily Arctostaphylos spp.) and the other dealt with geophytes, ie. plants that arise from bulbs or corms. In this post I'm going to summarize the article on Manzanitas and talk about how it applies to gardening with natives and to my garden in particular.

New Growth on Del Mar Manzanita (Arctostaphylos glandulosa ssp. crassifolia) in my front yard

The Manzanita article was titled Diversity and Evolution of Arctostaphylos and Ceanothus by V. Thomas Parker. The author explained that there are two main lineages of Arctostaphylos, and these are differentiated by how they respond to fire. The two types are burl-formers and obligate seeders. This in itself is a fascinating fact. It suggests that there was a parent taxon somewhere in the past 1.5 million years that was subjected to episodic fire, with some of its offspring responding one way and others responding another way. 

Burl-formers are also called stump-sprouters and crown-sprouters. The burl is an enlarged woody rootstock or junction between the trunk and the roots. Here's how the sprouters work: these species are capable of producing new growth from the burl after a fire as long as the burl is not irrevocably damaged. The top of the burl usually gets charred, but the rest of it is very tough and mostly underground, so it's usually okay unless the fire is unusually hot. New growth comes out from the undamaged part of the burl. All branches can be destroyed, but if the burl is not totally burned up new branches will sprout out almost immediately after the fire, often within days. Burl-formers do produce seeds, and some of them do germinate after a fire, but the majority of seedlings die within a year or two (unless the fire is exceedingly hot and a large number of burls are destroyed). In general, seedlings can't complete with re-sprouting burls that have huge, intact root systems.

I should mention here that Arctostaphylos isn't the only genus that uses stump-sprouting after fires. Heteromeles arbutifolia (Toyon) and Xylococcus bicolor (Mission Manzanita) also stump-sprout, as do many others. It's a fairly common chaparral adaptation to fire.

Arctostaphylos rudis (Sand Mesa Manzanita) in San Luis Obispo County.
Photo by Akos Kokai [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)]

Manzanitas that are obligate seeders do not form a burl and are typically killed outright by fire. However, obligate seeding species of Arctostaphylos outnumber the sprouters, and their response to fire is equally effective because they produce lots of seeds that are primed to germinate by the chemicals in smoke. Germination is not immediate, but when the first rains come after the fire, germination is rapid and widespread. There are no old plants to compete with the seedlings, and an entirely new generation is created. Thus, both lineages of Arctostaphylos are able to come back after a fire. There are limitations to each approach, but in a system that is not too screwed up by people both lineages do well. The key difference between the two lineages is what it means for their genetics. This is where it gets really amazing.

Los Padres National Forest, Aug. 2009
Photo by Airman 1st Class Andrew Lee

The burl-formers don't experience a lot of genetic change over time because the original plants are simply regenerating themselves. The fire has changed nothing in the genes of these plants. On the other hand, obligate seeders experience a lot of genetic change with each fire. It isn't that fire directly causes genetic change. Rather, fire kills all the adult plants in the burned area, wiping out that generation in that place. The thousands of seeds which have lain dormant in the soil for many years or decades will have slightly different genetics from their parents, the result of unique combinations of pollen and ovules. It makes for essentially 100% genetic turnover in the local population. The new genetic diversity created by this event creates some plants that are very well suited to their environment and others that are not so well suited. It should also be noted that Manzanitas of both lineages tend to hybridize readily, and over time all this cross-fertilization and hybridization by obligate seeders will produce enough genetic variation to form new taxa (species, subspecies and varieties). Hybridization doesn't mean as much for the burl-formers because production of new plants from seed is less important to their short-term survival. 

The behavior of obligate seeders is most dramatically seen in the Arctostaphylos-dominated chaparral communities of the central coast. I'm going to throw around some numbers from Parker's article. California is home to about 95 taxa of Arctostaphylos; 42 of these occur in the narrow coastal band between the San Francisco Bay and Monterey Bay; 32 of these are referred to as "narrow endemics" that are restricted to very small geographic areas. Plus, there are several more narrow endemics between Monterey and Santa Barbara. Many of these are are on the CNPS Inventory of Rare and Endangered Plants. Why is this a big deal? Virtually all of these narrow endemic Manzanitas are obligate seeders, and this is the key to their rarity. 

In Monterey County alone the following 14 rare taxa are found (each species name below is clickable and will take you to the appropriate page on Calflora):

• A. andersonii (Heartleaf Manzanita)
• A. cruzensis (La Cruz Manzanita)
• A. edmundsii (Little Sur Manzanita)
• A. gabilanensis (Gabilan Mountains Manzanita)
• A. glutinosa (Shreiber's Manzanita)
• A. hookeri ssp. hookeri (Hooker's Manzanita)
• A. hooveri (Hoover's Manzanita)
• A. luciana (Santa Lucia Manzanita)
• A. montereyensis (Toro Manzanita)
• A. obispoensis (Serpentine Manzanita)
• A. parjaroensis (Pajaro Manzanita)
• A. pechoensis (Pecho Manzanita)
• A. pilosula (La Panza Manzanita)
• A. pumila (Dune Manzanita)

What the above points out is the fairly incredible amount of genetic diversity generated by the obligate seeders of the central coast. In every little micro-climate and micro-niche there is a Manzanita that is specifically adapted to the conditions found there. It is also noteworthy that in this central coastal strip fire is currently not as common as it is in warmer and more arid parts of the state. Burl-formers would have no particular advantage in the absence of fire, but also the obligate seeders would have fewer opportunities to get rid of the old generation and start a new one. Parker states that these narrow endemics have evolved quite recently, in the last 10,000 to 20,000 years, suggesting that this amount of speciation occurred very rapidly as a result of just a few major fire events.

One implication of the foregoing is that the obligate seeder taxa are potentially not very stable in the long run. A big fire in Monterey County could wipe out one or more rare species, and the seedlings that would emerge after the fire would be different from the parents in ways we cannot predict. All of these rare species will have hybridized with each other and with more common species. Each seedling would have slightly different genetics, and it would take years to see which ones would survive and dominate. The chances of the original species reestablishing themselves after such an event is slim.

Manzanita in My Garden. I live in San Diego County, not the central coast, so the Arctostaphylos species here are naturally going to be different from those in Monterey or Santa Cruz. There are some rare species of Manzanita in my region, but only a handful compared with the 14 found in Monterey County. One of San Diego's rare taxa is A. glandulosa ssp. crassifolia (Del Mar Manzanita), and I am fortunate to have a nice specimen of it (shown in the photo below). The basic species A. glandulosa is quite widespread, occurring in the coastal strip from Oregon to Baja. However, ssp. crassifolia is limited to a very small ribbon of southern maritime chaparral between Torrey Pines and Carlsbad. You can see it on the Calflora map. Zoom in on San Diego County to see exactly where it is found. A. glandulosa has a number of other subspecies as well. Some are common and some are rare. An academic paper on the species states: "Particularly in the southern half of its range it exhibits complex patterns of morphological variation that have long presented taxonomic challenges." (Subspecific Variation in the Widespread Burl-Forming Arctostaphylos glandulosa, Jon E. Keeley, Michael C. Vasey and V. Thomas Parker. Madrono, Vol. 54, No. 1, pp. 42–62, 2007).

A. glandulosa ssp. crassifolia with flowers and fruit in my front yard

Is ssp. crassifolia a sprouter or a seeder? It does both. It has a burl and after fire it sprouts from the burl. But the seeds are also activated in response to fire. This dual approach is called Facultative Seeder. Perhaps this helps explain the rarity of ssp. crassifolia, as well as the taxonomic challenges of the many subspecies. Under ordinary conditions it would be expected that stump sprouting would dominate after fires, producing genetic stability. Seedlings would come up but these would typically not survive. But suppose there were some fires in the past which killed all the mature A. glandulosa plants in a given area, destroying all the burls. This can happen in an extremely hot fire. Then recruitment from seeds would have taken over. The new genetic diversity contained in these seeds would have created numerous new versions of A. glandulosa, some of which would have been especially well suited to a particular soil or micro-climate. The one that became ssp. crassifolia would have been a seedling that was best adapted to the sandstone soil and mild, maritime climate where it occurs, while other versions of the same species would be better adapted elsewhere. In response to subsequent low-intensity fires, individuals of ssp. crassifolia would stump sprout, maintaining stable genetics in the subspecies. I would expect ssp. crassifolia to remain stable until the next catastrophic fire in which most or all of the ssp. crassifolia burls are destroyed. Then we might get entirely new subspecies or varieties arising from all the seeds in the soil. In this scenario, unburned individuals of ssp. crassifolia, such as those in gardens, might be the only source for the original genes of the taxon. This is just speculation on my part and I may have it completely wrong, but I think it makes sense.

Mojave Yucca (in bloom), Dudleya, Summer Holly, Del Mar Manzanita, and Toyon in my front yard

Taxonomists must go crazy trying to sort out all these variations in Arctostaphylos. Or maybe they love it. In addition to all of these species, subspecies and varieties, we have other genera that exhibit similar traits, including Comarostaphylos, Ornithostaphylos, and Xylococcus, all in the same family. In a more recent Fremontia (May 2015), Lee Gordon and several co-authors examined the reproductive behavior of Mission Manzanita (X. bicolor). In view of its apparently low seedling survival rate, they asked whether Mission Manzanita is in decline. It, too, is concentrated in San Diego County. Over the eons it seems to have been more stable genetically than Arctostaphylos. I say that because there is only one species in the genus, and no subspecies or varieties. My guess is that it is a Facultative Seeder that can reproduce from seed but seldom needs to, much like Del Mar Manzanita. But unlike Del Mar Manzanita it never experienced a fire that wiped out a whole generation and triggered massive seedling production, with its attendant explosion of genetic diversity. Is this possible? I don't know. Once again I am just speculating. But it is indisputable that Mission Manzanita relies heavily on stump-sprouting, rarely reproducing from seed, and appears to remain extremely stable genetically. Or at least it looks that way to me.

The Bottom Line is that plants must use sexual reproduction (seeds) in order to achieve genetic variability. They can't get any variation from stump-sprouting. The same could be said of plants that reproduce vegetatively, such some of the cholla cacti which produce clones. But stump-sprouting isn't even reproduction, it's just continued growth of the same individual. Stump-sprouting gives individual plants the ability to live a long time and to withstand most (but not all) fires. Seed reproduction, on the other hand, gives the species as a whole the opportunity to develop new genetic strains which may have enhanced survival value in a given place and time. So the Arctostaphylos species in California give us an interesting picture of the adaptive trade-offs between these two different strategies for responding to fire.

In Part II I will talk about the geophytes and their unique response to fire.

Strange New Resident

The other day I found this thing on our lime tree. Why do we have a lime tree in my mostly native garden? My wife wanted it. So anyway, this thing looked like a very large bird poop, but I knew it wasn't that. After more looking I found a second one. Here's my best photo of it.

I believed I'd seen these before but couldn't remember exactly. After consulting with my entomologist friend, I learned that they are the larvae of a Giant Swallowtail butterfly (Heraclides cresphontes). Then I recalled briefly seeing an adult swallowtail of some type flitting about the lime tree about two weeks ago. It was an impressive butterfly but I couldn't identify it, so I grabbed the camera and shot a few pictures while it was flying about. They aren't great pictures because it wouldn't stop moving, but they do document what is was and the egg laying activity (see photo further down).

Back to the larvae, they are called Orange Dogs. I believe the orange reference is to the fruit because they feed on citrus plants and they clearly aren't orange in color. As far as the dog reference, look at the face on this one. The larva's resemblance to bird poop is probably pretty effective camouflage. They are also distasteful to birds and can emit a foul odor if threatened.

This species was previously quite rare in California. They have spread from the southeast through Texas and the southwest and are now becoming more established here. They reportedly don't do significant damage to plants. I'm relieved at that because it means the big citrus growers won't be targeting it for eradication. Still, commercial citrus groves are probably no good for this species because they are sprayed with so many pesticides. Organically grown citrus in home gardens is probably their best place for egg laying.  

The adult is said to be the largest butterfly in North America, with a wing span of up to 6 inches. I can believe it based on the size of the larvae and the one I saw laying eggs in October.The chrysalis will resemble a dried, curled up leaf which may make it difficult for me to find. As an adult it will only live about 2 weeks, but that should be long enough for it to find a mate and lay more eggs.

A funny thing about this photo is that there is already a larva on a leaf in the upper right corner of the photo. I never saw it when I was taking the photo because I was focused on the butterfly, and I never saw it when reviewing the photos. I only saw it after cropping the photo to include it here. It makes me think about how many interesting thing I probably miss every day.