Plants of Southern California


Fig. 1. Nutlets (top view)

Pectocarya heterocarpa


Pectocarya peninsularis


Fig. 2. Nutlets (bottom view)


 

Table of Contents

Abstract (Summary)
Introduction
Geographic Distribution of These Taxa
Distinguishing Characteristics

 


Abstract (Summary)

Pectocarya heterocarpa and P. peninsularis are very similar species, and are difficult to separate unless you know exactly what to look for. This page shows their distinguishing characteristics, their ranges, and pictures of both species showing some of their variation.

Introduction

Pectocarya heterocarpa is a widespread species in southern California, whereas until recently there were very few known locations of P. peninsularis, whose range is primarily in the north half of Baja California, befitting its scientific name (for the Baja peninsula) and its common name of Baja pectocarya.

The 1974 Flora of Southern California by Munz does not even list P. peninsularis. Beauchamp, in his 1985 Flora of San Diego County, gave P. peninsularis as being rare; below 300 m; northwest of Narrows; Borrego Valley. Oddly, though, the 1985 Duffie Clemons flora of Anza-Borrego Desert State Park does not include that species. The 1993 first edition Jepson Manual gave it as occurring in DSon.

When I searched for vouchers on 14 March 2008, I found a total of only eight vouchers in California, five in San Diego County, all in the Carrizo Valley, and three in the Coachella Valley of Riverside County.

However, there are now 23 vouchers of this species online, with three vouchers in the Borrego Valley and another in Ocotillo, adding two new locations to the voucher distribution.

This improved knowledge of the distribution of this species has resulted from at least two sources. First, the San Diego County Plant Atlas project has resulted in a number of new specimens from different areas, with all the determinations made by Jon Rebman. Second, the Pectocarya website by Mike Simpson, and the results of his and Ron Kelley's study of this genus, have resulted in better understanding of the characteristics of these species for voucher determinations.

Perhaps the main difficulty in recognizing that P. peninsularis occurred more frequently in southern California was that it is quite similar in many ways to P. heterocarpa, enough so that even the determination of vouchers is somewhat difficult. The 1993 Jepson Manual key is in fact misleading or incorrect for two of the three characteristics used to separate these species in the key, at least for southern California specimens, and the illustrations there for the species don't adequately show the differences in the nutlets.

Although I occasionally had come across plants in the Borrego Desert that seemed a bit different from usual P. heterocarpa, primarily in having a pedicel not partially fused to one nutlet, they never satisfied more than that one of the three characteristics used in the Jepson Manual key. Furthermore, their nutlets didn't look any more like the Jepson Manual illustration for P. peninsularis than they did that of P. heterocarpa.

Furthermore, after finding a clear P. heterocarpa along Henderson Canyon Road, along with a voucher of "P. peninsularis" from that same location, I asked Mike Simpson to take a look at that voucher, and it turned out to be misdetermined P. heterocarpa.

Hence I had largely given up on the possibility of finding P. peninsularis in the Borrego Desert.

Fortunately, on 13 March 2011, on a survey with Mike Crouse and myself, Kate Harper found a specimen that appeared to have the free pedicel characteristic of P. peninsularis, and strongly encouraged me to examine it further at home to check it out.

This time, when I found the pedicel of this specimen free of any nutlet, I checked the pictures on Simpson's page. To my surprise, the nutlets shown there looked very similar to the nutlets on this sample, and quite different from the nutlets of P. heterocarpa. Furthermore, in checking vouchers, I found the new vouchers of P. peninsularis from the Plant Atlas, including one from essentially the same location as Kate's plant.

I then went through my pictures and vouchers of my previous "P. heterocarpa" determinations in the Borrego Desert, which was the motivation for producing this page, and the source for the pictures here.

Geographic Distribution of These Taxa

The geographic distribution of these two species, from vouchers with coordinates, are given in Figs. 3 and 4:


Fig. 3. Plot of voucher locations for P. heterocarpa.

Fig. 4. Plot of voucher locations for P. peninsularis.

The plots above were from data provided by the participants of the Consortium of California Herbaria (ucjeps.berkeley.edu/consortium/; Sun Mar 20 2011).

See also the distribution maps for Baja California in Simpson's page on P. peninsularis.

Distinguishing Characteristics

Size of plant. I've found both species growing side by side in two different locations. Interestingly, in both cases, the stems of P. peninsularis were significantly smaller and more delicate than those of P. heterocarpa. See pictures of specimens from Coyote Canyon Wash (P. peninsularis on left), and from Collins Valley (P. peninsularis on bottom).

Number of fruit with four nutlets. Many, but not all, of the stems of P. peninsularis I've seen have relatively few fruit with the full four nutlets, with many more fruit with one to three nutlets. In contrast, most of the stems of P. heterocarpa have many fruit with four nutlets.

Pedicel attachment to the nutlets. As seen in the pix at the top of this page, the pedicel of P. peninsularis attaches to the nutlets only at the point where all the nutlets originate, coming in at an angle close to perpendicular to the plane of the nutlets. In contrast, the pedicel of P. heterocarpa "slides in" to that same location, coming in at a very small angle to the plane of the nutlets. The difference in the angle is because almost half the pedicel is fused to the nutlet closest to the stem.

The difference in the shape of the pedicel is illustrated in Fig. 5:


Fig. 5. Picture showing the fused portion of the pedicel for P. heterocarpa, with an illustration of the shape of the pedicel for P. peninsularis. The piece of paper has a width of 1.0 mm, and is used to illustrate the free portion of the pedicel. Note that the pedicel for P. heterocarpa is not evident at the point where all the nutlets meet, which is the only point where the pedicel of P. peninsularis meets the nutlets.

Angle between the pairs of nutlets. This was what confused me the most about P. peninsularis, and was the strongest characteristic that prevented me from recognizing it before. The Simpson / Jepson Manual Second Edition key says that the nutlets of P. peninsularis are gen straight in 1 plane, which is not correct for the specimens I've seen, whereas the nutlets of P. heterocarpa are curved in 2 planes.

The meaning of the curvature in two planes is shown in Fig. 6:


Fig. 6. Picture showing the angles between the pairs of nutlets of P. heterocarpa. If you think of the nutlets as unfolding from their original joined position in the ovary, they unfold in two pairs, and the pairs are rotated from each other by an angle close to 90°.

In the fruit at the right, imagine sighting along the upper pair of nutlets from a position immediately behind the rightmost nutlet, so that the other one in its pair is directly behind it. The inside part of those nutlets, away from the calyx lobes on the other side of them, would then face up.

From that position, you would then see that the other pair of nutlets face to your left, at an angle of 90° from the upper pair of nutlets. That angle is explicitly shown as a right angle (the little square inside two perpendicular lines) on the set of nutlets at the left in the picture.

The nutlets I've seen for P. peninsularis are most distinctly in two planes, but at an angle of about 60° instead of 90°; see Fig. 7. It is very difficult to distinguish the difference in these angles, so although this difference exists, it is not very useful unless you can make that distinction. Mike Simpson says that he has found it hard to tell the difference between these species for this characteristic as well.


Fig. 7. Picture showing the angles between the pairs of nutlets of P. peninsularis. The upper pair of nutlets faces essentially straight up, whereas the lower pair of nutlets faces toward the camera, making an angle closer to 90° than to zero degrees.

Curvature of the nutlets. This is a strong distinction between the species, but it is not well described by the Simpson / Jepson Manual Second Edition key. The nutlets of P. heterocarpa are said to be curved, one pair incurved, the other pair recurved, whereas the nutlets of P. peninsularis are said to be gen straight, all spreading ± flat. The sense of this key is correct; the nutlets of P. heterocarpa are significantly more curved than those of P. peninsularis, as seen in the pictures at the top of this page. However, some of the nutlets of P. peninsularis are clearly curved, as seen in the pix above. But rather than being curved throughout, like the nutlets of P. heterocarpa, they are closer to appearing bent at one point in the middle of the nutlet, as if hinged at that point.

Ornamentation of the nutlets. Ornamentation is just a word to describe what the nutlet inner surface looks like. For Pectocarya nutlets, the ornamentation consists of what looks like a gum line, and what look like teeth projecting out of the gum line.

I've always had trouble with the Jepson Manual First Edition key in how it describes the nutlets, and have relied more on the illustrations in the Jepson Manual. I suggest you do the same, and simply look at the pix on this page to see the fairly clear difference between these two species.

Sepal shape. The keys state that the lower 3 sepals are ± equal for P. heterocarpa, and unequal for P. peninsularis. I haven't seen any real difference between the species in the few fruit I've analyzed in detail. Mike Simpson says that he has found it hard to tell the difference between these species for this characteristic as well.

More information. For more information about both of these species, and much better close-up pictures of the nutlets, see the Simpson pages on P. peninsularis and P. heterocarpa.


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Copyright © 2011 by Tom Chester
Permission is freely granted to reproduce any or all of this page as long as credit is given to me at this source:
http://tchester.org/plants/analysis/pectocarya/species.html
Comments and feedback: Tom Chester
Last update: 20 March 2011 (link added to Borrego Desert Species page 12 February 2013)