Amsinckia intermedia and A. tessellata, Fiddlenecks
Table of Contents
Introduction
Geographic Distribution
Elevation Distribution
|
|
| Fig. 1. Side-by-side stems of Amsinckia intermedia and A. tessellata growing in close proximity in Plum Canyon on 7 April 2019, showing how much larger and robust the inflorescence of A. tessellata was there compared to those of A. intermedia. The difference in size and robustness is generally, but not always, true. The key to separate these two species is that A. intermedia has 5 equal-width calyx lobes, and A. tessellata has 3 to 4 lobes, with at least one lobe twice the width of the others due to fusion of what once were separate lobes in its ancestor.
Photographs by Tom Chester; Kate Harper suggested photographing the inflorescence of the two species side by side. Click on the pictures for larger versions. |
Introduction
Amsinckia intermedia = A. menziesii var. intermedia, common fiddleneck, and A. tessellata, bristly fiddleneck, are both fairly widespread in the Borrego Desert, as well as in California. A. intermedia is mostly a coastal and montane plant that extends into the desert edge and the desert mountains, whereas A. tessellata is mostly a desert taxon that spills into the adjoining mountains, and also lives on the dry side of the coastal ranges.
These two species are commonly confused in the Borrego Desert, with a significant fraction of the iNat observations there of the two species misdetermined. Worse, a number of the iNat observations of the two species here cannot be reliably determined since they don't show the key distinguishing characteristics well, and the geographic distribution of the two species here is almost completely overlapping.
Amsinckia intermedia and A. tessellata are a bit frustrating to botanists, since they can be separated only when in flower or fruit. Even when they are in flower, though, these two are often confused since the difference is only apparent by looking carefully at the calyx lobes.
A. intermedia has 5 equal-width calyx lobes, and A. tessellata has 3 to 4 lobes, with at least one lobe twice the width of the others due to fusion in this species of what once were separate lobes in its ancestor; see Fig. 1. Sometimes (not always) the double-width lobe is notched at the tip, indicating it evolved from the fusion of two formerly-separate lobes.
It is somewhat difficult to examine the calyx lobes in the field, since in bud and flower the calyx lobes are close together and very prickly to examine by hand. But it can be done, especially with a tool such as a pencil tip to tease apart the calyx lobes. Much easier is that with practice, one can fairly quickly learn to visually scan the calyces to spot whether one calyx lobe is twice the width of the others or not in at least some of the flowers in a given inflorescence.
It is also generally easy to examine the calyx lobes in fruit, when the lobes naturally separate. The mature nutlets are also different, tubercled for A. intermedia vs. cobblestone-like (tessellated) for A. tessellata.
If you are lucky enough to be in an area that has both species, it is often easy to separate the two species from a considerable distance, since A. tessellata is generally a larger and more-robust plant; see Fig. 1. But if you don't have the two species growing together, it is difficult to use this difference, since both species can have a huge variation in size and robustness.
It is much more difficult to confidently separate the two species in photographs, even ones that try to target the differences. Counting the number of calyx lobes in a photograph is generally impossible, since the flower hides the lobes in views from the top of the flower, and some lobes are hidden in a side view. Worse, the relative width of the calyx lobes is difficult to ascertain in most camera views, since a face-on calyx lobe will appear to be wider than its neighboring angled calyx lobes. The double-wide calyx lobe of A. tessellata might also be hiding behind its equal-width lobes. If you look carefully at some of the non-labeled calyces in Fig. 1, you'll see that that the double-width lobe is not apparent in every flower for A. tessellata, and that it might be easy to conclude that some calyx lobes for A. intermedia are double-width.
The floras claim that the flowers of A. intermedia are "±orange, generally with 5 dark spots", and those of A. tessellata are "yellow", with no mention of any dark spots, but this flower color difference does not seem to be the case in the Borrego Desert, and both species generally have dark spots. Fig. 1 shows there might sometimes be a subtle difference in the flower color, but a quick glance at photographs of many other plants show there is much more overlap in color between the two species than there are differences. Dark spots are present inside the corolla of most flowers of both species. See, for example, this yellow-orange corolla with five dark spots that is clearly from A. tessellata due to its three calyx lobes. Compare it to this more yellowish corolla with faint dark spots that is clearly from A. intermedia due to its five equal calyx lobes. Those flowers would be both misdetermined if one just went by the claimed color difference in the floras!
One thing you don't have to worry about is these two species hybridizing, since they have incompatible chromosome numbers (2n=30, 34, 38 for A. intermedia; 2n=24 for A. tessellata). In fact, A. intermedia is usually self-pollinated, which has resulted in it consisting of separate lineages that are highly variable, with, believe it or not, over 100 named variants!
Geographic Distribution
Fig. 2 shows the geographic distribution of these two species in the Borrego Desert region from my observations, vouchers and iNat observations, and Fig. 3 shows a histogram of the elevations for these two species. Only vouchers and iNat observations with accurate locations are plotted. I've also reviewed the western-most iNat observations of A. tessellata, and removed ones that are not clearly A. tessellata. Although some remaining iNat observations are almost surely misdetermined, these maps agree overall with maps made just from my observations and vouchers. The misdetermined iNat observations are in areas where both species are present, so they don't affect the overall distribution.
The number of A. intermedia points in these plots are 33 from my observations; 99 from vouchers with good locations; and 131 from iNat observations with good locations. Jon Rebman was the dominant collector, with 26 vouchers; Larry Hendrickson was next with 19 vouchers. Fred Melgert and Carla Hoegen were the dominant iNat observer, with 43 observations, with no one else having more than 11 observations.
The number of A. tessellata points in these plots are 20 from my observations; 33 from vouchers with good locations; and 133 from iNat observations with good locations. Jon Rebman was the leading collector, with 7 vouchers; Larry Hendrickson was next with 6 vouchers. Fred Melgert and Carla Hoegen were the dominant iNat observer, with 32 observations, followed by Don Rideout with 16 observations.
The number of Amsinckia points from my 464 Borrego Desert surveys is very low, since Amsinckia species can only be identified when in flower or recent fruit.
| 
|
| Fig. 2. The geographic distribution of A. intermedia (left) and A. tessellata (right) for the Borrego Desert area. Although there is almost complete overlap of the two species in the Borrego Desert area, the distribution of A. tessellata is clearly shifted eastward compared to the distribution of A. intermedia. I.e., if you put the two maps on top of each other, and then switch between them repeatedly, the main distribution of the red dots for the two species will appear to shift east-west.
The geographic east-west shift between the two species is verified by the histogram of elevations in Fig. 3 which shows that A. tessellata is on average found at the lower elevations on the east. The two isolated westernmost locations of A. tessellata are both from vouchers, one set from Lucky 5 Ranch in the Laguna Mountains by Jon Rebman, and one from North Volcan Mountain by Tom Oberbauer, both determined by Jon Rebman and so are highly likely to be correctly determined. A. tessellata is given as occurring up to 7500 feet elevation in California, so these are likely just the outlying edge of the species in our area. There are many more locations of A. intermedia to the west of the points shown. Click on the maps for larger versions that are on the same scale, and can be blinked against each other. | |
There are only a small number of Borrego Desert locations that appear to contain only one of the two species. The Little Clark Dry Lake area, the Borrego Mountain area, and the Carrizo Badlands area appear to have only A. tessellata. The San Felipe Valley, the Granite Mountain area, the Cuyamaca Rancho State Park Area, and the Pine Valley, Boulder Oaks, Campo, and McCain Valley area appear to have only A. intermedia. Of course, only A. intermedia occurs to the west of its red dots in the above map; see the map of the two species using all San Diego Herbarium vouchers (note that this map includes vouchers with poor locations, so it appears to show some locations not present in the maps in Fig. 2).
Elevation Distribution
Fig. 3. Histogram of the elevations for A. intermedia and A. tessellata. A. tessellata is the most common of these two species below 1000 feet elevation, with A. intermedia the most common from 2000 to 3500 feet elevation. It is a bit curious that the two species have comparable numbers between 3500 and 6000 feet, so this might be a sign that those observations should be examined more closely.
The elevations are from the highly-accurate National Map.
Voucher data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/) on 11 March 2021.