Feb 18, 2014
In early February of last year I came across a single manzanita bush flowering near a spring at the southern end of the Santa Rita Mts. This started an interest in these plants and their associates. Over the last year I’ve collected manzanita plants, berries and leaves from various locations all over Arizona. I have also been writing about my findings in this blog. In this article I hope to summarize what I know of these fascinating plants.
The genus Arctostaphylos is mainly found as two species in Arizona, A. pungens and A. pringlei. In addition, A. patula is found on the North Rim and A. ursa-uvi is found in the Chuska Mts. on the Dineh Nation. Of the two most prevalent species, A. pungens has a wider distribution which continues down into Mexico (SEINet, ). In California, A. pringlei has been found to hybridize with other species of Arctostaphylos (Chester, 2008), so one of my first interests was to see if the two species were sympatric in Arizona. I can safely say that they are. I have found the two plants growing close together in many instances and in one case, they seemed to be growing from the exact same spot (Beaver, 2013) As to whether they are hybridizing, that is a much harder question. One of the problems is the range of variation of different characteristics of the two plants, especially A. pringlei.
Distribution of A. pungens and A. pringlei in Arizona
The map below shows specimens of each species collected in Arizona (SEINet, ). Be aware that the accuracy of some of the coordinate data is low and some are mistakes. The map does give a general view of the distributions of the two species.
It should be noted that populations are in no way contiguous and have been isolated for at least 8,000 years to each mountain range or “Sky Island.” This is especially true of A. pringlei.
To find elevation distributions I took the SEINET data (SEINet, ) and used only the coordinate data. Then I threw out all the coordinates that had a stated accuracy greater than 10 km and all those that looked wrong (coordinates that were in the desert, etc). Then, to get some elevation consistency, I ran the coordinates through the GPS Visualizer (Schneider, 2013) which uses DEM data. The following box plots show the result.
This shows that the overall range for A. pungens is greater than A. pringlei, especially the lower range, and that the mean elevation for A. pringlei is slightly larger than A. pungens. The mean for A. pungens is 1581 m. while the mean for A. pringlei is 1735 m. The difference is 154 m. which is about a 505 ft. difference in elevation.
There are two reasons to be suspect of this data.
- The coordinate data is pretty suspect and thus the elevation data could be off.
- The vast diversity of landforms within Arizona makes this data suspect. At the very least, the data has to be broken down into mountain ranges as each range and perhaps each slope exists as a separate distribution entity.
What is needed to give a better idea of the distribution is to walk a transect at single or multiple locations. I have no doubt of sympatry, I have found many regions of exclusive A. pungens but have also found A. pungens around even large stands of A. pringlei.
Flower structure and flowering
I didn’t do any measurements of the flowers last year. Some field characters that could be measured are:
- diameter of the opening
- length flower
- color of flower
- color of bract
- hairiness of bract
- glandularity of bract
- color of pedicule
- hairiness of pedicule
- glandularity of pedicule
- number of flowers in the inflorescence
One variation in the flower structure I did notice. Although A. pringlei in California are typed by their pink bracts, I noticed both pink and white bracts on A. pringlei in Arizona.
Another major character is the timing and amount of flowering. It has been shown that in California, for Arctostaphylos glauca and Arctostaphylos glandulosa, the amount of flowering is correlated to the last season’s rainfall (Keeley, 1977). California has one rainy season in the winter, although near the coast, the summer fog can be considered a second rainy season (Azevedo, Morgan, 1974). Arizona has two rainy seasons, winter storms from the Pacific and summer storms from the Gulf of Mexico.
In the histogram below I show the various flowering times found in the Arizona SEINET data (SEINet, ). I cleaned-up the column for reproductive state to make it a true character column. I also added flowering if the flowers were mentioned in the description of the plant or in the notes.
The flowering data is a little more structured than the elevation data with A. pungens peaking in April and A. pringlei peaking in June. The distribution of the data shows both plants having blooms almost any time of the year. These outliers are not just mistakes but represent advantageous blooming with variable rains. I found a few flowers of A. pringlei in bloom on February 2 in the Catalina Mts. There were A. pungens in bloom all around. Thus the two plants can not only share physical space but also have a potential to share pollen.
Fruit structure and fruiting
Manzanita fruit consists of a fleshy berry with a hard endocarp. Fruiting time varies wildly as the fruit can stay on the plant into the next season. The rate and exact conditions for fruit drop is unknown. The endocarp structure is one possible character difference between different manzanita species. The endocarp can be a solid stone containing 4 to 10 seeds (Keeley, 1977) or it can break into several parts containing one or more seeds. Species of manzanita can be typed as to whether the endocarp is solid or breaks apart.
(Rancho Santa Ana Botanical Gardens, 2004)
A. pungens is typed as a broken endocarp while A. pringlei a solid one. By gathering and strippinng berries in Arizona I have found a great deal of variation in both plants (Beaver, 2013). Each chunk of endocarp can contain 4 to 10 seeds but evidence is that each chunk will produce only one plant from however many viable seedlings (Keeley, Zedler, 1978). Because of this, these chunks are called propagules (Keeley, 1977). There seems to be a tradeoff between the number of propagules and the number of seeds in each propagule. What is causing this tradeoff is unknown but rainfall, fire, persistence in the seed bank, predation, and dispersal come to mind. For whatever reason some species of manzanita produce less number of propagules with more seed potential while other species produce more propagules with less seed potential.
I have collected leaves from both species of plants all over the state. I have not made an analysis of them but can mention a few tendencies I’ve noticed.
- Leaves of A. pringlei look more variable in shape than leaves of A. pungens.
- Young leaves of A. pringlei look very much like the leaves of A. pungens.
- Leaf color is perhaps the most significant difference between the two species. I am trying to think of a way to quantify leaf color in the field, color perception is not very accurate at best.
Hairiness and glandularity
Did no specific measurements of either of these two characters but did notice more variation in A. pringlei. I don’t know, for instance, if this difference is based on the time of the season or represents variability or even two different phenotypes. Again, a field method to quantify both these characters would help greatly. Also, this needs to be broken down into the various important plant parts: leaves, flower structures and small or young branches.
I did notice more variation in bark than I thought I would, though not nearly the variation I’ve noticed in Arbutus. The smooth red bark sometimes has a peeling papery outer skin and there is a definite difference between the young growth of A. pringlei, which has a green bark which turns red in a checkered pattern as it ages and A. pungens, which has the smooth red bark from the first.
Association is interaction between different species. Associations are typed by how the interaction affects the fitness of each associate. For instance, a male insect using the branch of a bush to perch is using the plant’s height to it’s reproduction advantage for finding females. The insect gains a fitness advantage but the plant gains nothing. In the simplest case each individual of each pair of associates can have a change of fitness of - or 0 or +. Of particular interest is mutualism, in which both associates have a fitness gain, how it evolved and how it is maintained (Bronstein, 1994).
Association is also important to community structure where here the measure is amount of diversity. Predators may reduce significantly the amount of prey but they can also increase the diversity of a community by controlling the prey’s population.
Manzanita flowers are bisexual and provide insect hosts with pollen, nectar and the flower parts themselves. The main difference between the two species in Arizona is the glandularity of A. pringlei which could be a defense against insects. A. patula in a northern California study has been found to associate with 19 orders and 169 families of arthropods with over 500 taxa were identified below the family level (Valenti, Ferrell, Berryman, 1997).
Bees collect both pollen and honey by crawling into the mouth of the bell-shaped flower which hangs downward. Thus the opening is down in relation to the ground. The petals of the flower are fused so there is only one opening. Bees also “rob” nectar by cutting a slit near the base of the flower. Thus they can collect nectar without contacting and spreading pollen. There are also round holes apparently cut by caterpillars (see below) that allow access to the nectar. Bees of many a genus visit A. pungens in Arizona (Richardson, Bronstein, 2012). One is the super generalist European honeybee (Apis melioflora). Arctostaphylos is in the family Ericaceae and most of the genus of this family has a similar flower structure. The blueberry bee (Osmia sp.) is a close associate of species of Ericaceae that have these type of flowers.
Because thrips cannot curt open manzanita flowers themselves, they must wait for flower opening or for holes or slits cut in the flower. Thrips have been shown to pollenate A. uva ursi in Europe (García‐Fayos, Goldarazena, 2008) and thrip pollenation is being studied here in Tucson (Eliyahu, 2013). I have found thrips in A. pungens flowers last year and found clouds of them around a bush this January.
Thrips of a single species, Orothrips kelloggii, are associated with all Arctostaphylos (Hoddle, Mound, Nakahara, 2004).
Brown Elfin (Callophrys Augustinus) and other Lepidoptera
Many Lepidoptera visit manzanita flowers. These include both butterflies and moths. Caterpillar larvae also host this plant. So far, evidence suggests Brown Elfin (Callophrys Augustinus) and [beetles blog] on A. pungens. I have also see Blue Azure (Celastrina ladon) and a fresh hairstreak on A. pungens, so perhaps they associate as caterpillars.
I have found nothing in particular in the literature about A. pringlei. Brown Elfin is closely associated with A. pungens in Arizona and most importantly the caterpillars are flower eaters. They are the primary suspects for the creatures eating holes in A. pungens flowers. This hasn’t been proven or published yet. Brown Elfin are generalist herbivores over their North American range but they seem to specialize on A. pungens in Arizona. I went through the DesertLeps data for Callophrys Augustinus in Arizona and found no mention of them in association with anything other than A. pungens.
The Richardson/Bronstein data (Richardson, Bronstein, 2012) show several Diptera visiting A. pungens flowers. Gall aphids (see below) associated with manzanita are predated upon by flower fly larvae (Valenti, Berryman, Ferrell, 1996). This suggests a closer association if a fly associates at both of it’s life stages with the same plant.
I have not seen beetles on either of the plants although I have found seed damage on both A. pungens and A. pringlei in the Santa Catalina Mts.
Aphid galls are bright red swellings around the edges of manzanita leaves. I have found aphid galls on both species here in Arizona. A single genus of aphid, Tamalia, forms galls on manzanita. This genus also causes different types of galls in California on some manzanita species but I have found no evidence so far in Arizona (Companiytsev, 1997). Some four or five species of the genus have been identified including one specific to A. pringlei in California. The galls also house equilines, sister species which share galls but don’t initiate them (Miller, 1998). The galls also house predators, most particularly flower fly larvae (Valenti, Berryman, Ferrell, 1996). Galls are most prevalent on younger plants after a wildfire (Miller, Hatfield, Holden, 2012), (Sholes, Beatty, 1987).
I have found no ants on either species. Since there is evidence of Lycaenidae associated with manzanita there is the possibility of ant association as this family has about a 75% species association with ants.
I have found mention of coyotes, elk, deer, bear, wood rats, and other rodents eating manzanita in the literature (Keeley, Hays, 1976). Nothing specifically on this particular species but I have seen deer in the Hualapai Mts browsing on A. pringlei (Beaver, 2013).
Arctostaphylos means “bear berry” so there should be some association between them and manzanita. Black bears are particularly scarce in Southern Arizona and efforts to restore them in the Catalina Mountains met with tragedy. The map below shows black bear distribution in Arizona. The tan color represents the highest distribution. The big hole in the map is the two Apache reservations since this is Arizona Game and Fish. Notice that the Pinalenos Mts. have the highest distribution of bears in southern Arizona.
I have not seen birds eating any of the seeds and I have not found any reference to birds in the literature. If there are birds eating the seeds then there is probably some dispersal going on.
The two plants are defininetly sympatric and although they generally don’t share flowering times there can be situations when they do. A. pringlei can be distinguished by eye in a moving car from A. pungens but is much more variable in leaf shape, hairiness and glandularity.