The manzanita (genus Arctostaphylos) in the Catalina Mts. have had a fantastic bloom this spring. At the lower elevations starting at Molino Basin, the A. pungens have already bloomed and the berries are set and already starting to ripen. Higher up the A. pringlei are in full bloom at Manzanita Point and where the road goes through the large rocks above Windy Point. The two species are closely related and A. pringlei is sympatric with A. pungens throughout Arizona although A. pungens grows alone in the lower elevations and down into Mexico. The two species differ in their main flowering times although both take advantage of local conditions, summer rains, or freak rains to bloom throughout the year. A. pungens grow a pre-flower called a nascent inflorescence in the fall before winter so they can bloom early while A. pringlei flowers grow from buds in the spring. A. pringlei is one of the few (maybe only) manzanita species to do this (Keeley, 1997). A. pringlei have much larger flowers than A. pungens and are much pinker although most of the pink color is in the bracts and flower stems rather than the flower itself. A. pringlei also is covered with tiny hairs which extrude a sticky resin giving the plant a soft greyish-green appearance. These hairs are mainly on flowers and new growth with the leaves having a variable degree of hairiness. Cutting into a flower I noticed that the inside of the flower is hairy and sticky as well. Three adaptive uses have been proposed for these sticky resins. One is to trap insect pests. Another is to stick to larger pollinators to facilitate the transfer of pollen. A third is that the resin might melt over the surface of a leaf in the hot sun and thus protect it.
A. pringlei flowers, as seen below in the photographs, are covered with dead insects that have been trapped by the resin. Since the species flowers later in the spring, there are many more potential pests around. A. pungens‘ nascent inflorescence forms in the fall and is encased in a hard shell. The pant starts flowering in late January during the winter rains and before major insect blooms and the plant has surface hairs, but much sparser and not sticky. Insects trapped on the blooms also fall into the leaf litter and might provide with a bit of extra nourishment. I found many aphids on the new leaves, many trapped by resin. All manzanita have mutualist aphid (Tamalia) galls on them (Miller, 1998). These form on new leaves and I’ve seen these on both species although there were none on the plants I looked at and I’ve seen much fewer galls on A. pringlei than on A. pungens. It is believed that the galls on A. pringlei have their own species of aphids that have longer legs so as to step over the resin.
There were also live insects on the plants. I spotted a small beetle I haven’t typed yet crawling around the flowers with no fear of being stuck. This might be the source of the holes I’ve seen in the seed packages of both species. I spotted something moving in and out of a flower, some larvae, too big to be a thrip. I also saw what looked like a gall wasp (Cynipidae), there being a large oak growing nearby.
I saw a few pollinators but no honey bees, which is unusual. There was Osmia ribifloris, a bee associated with most manzanita and the bee or hover fly (family Bombyliidae, genus Bombylius). I got some good photos of it below. A bee mimic, it has a long proboscis with which it can sip nectar and long legs to grasp the flower. It seems ideally suited for this as it’s body never gets close to the surface of the flower. One photograph shows what looks like a resin droplet on the snout, a good place for pollen to stick.
Pollination is occurring as the seed set for these plants is always impressive. For plants, there is always the question of selfing. For other species of manzanita, the selfing rate has been found to be low. This doesn’t mean that this is true for all Arctostaphylos, the genus is so plastic in its characters that each species must be tested individually.
In examining some flowers that I had taken home, I noticed a hole cut in the bottom of one. Nectar robbing is common with A. pungen flowers and they often have these tiny holes (Richardson, Bronstein, 2012). Earlier in the year I saw a honey bee moving from flower to flower, never pollinating, but only visiting cut holes to steal nectar. I have never seen a cut hole before on A. pringlei, perhaps the rarity of this is due to those sticky hairs.So now there are perhaps five adaptive uses for these viscous hairs.
- Protection from herbivores
- A bit of nourishment
- To help in pollination
- To prevent nectar robbing
- To protect from excessive heat and sunlight