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Journal archives for November 2017

November 02, 2017

Croton list of Central and North Central Texas

Here is a list of the species that occur in Central to North Central Texas starting at around Austin west and San Antonio north. Unless otherwise stated, assume that all species listed have 3 styles divided once (for a total of 6 branches) and that the leaves are entire. Plants are listed from what appears to be most to least commonly observed in the area on iNaturalist.

C. monanthogynus: 2 styles each divided once (4 segments); abaxial sides of leaves appearing brown-dotted; low annuals often branching at the base and without a strong main stem (i.e., plants not robust, usually without a primary axis at maturity and widely branching).
C. lindheimeri: Sepals longer than fruit, the tips curving inward to enclose the fruit at maturity; leaves often cordate at the base, rarely serrated; wooly annuals typically with a single main stem (i.e., plants robust, usually with a primary axis and not widely branching), not typically branching at the base.
C. glandulosus: Leaves serrated, low annuals often branching at the base and without a strong main stem (i.e., plants not robust, usually without a primary axis at maturity and widely branching).
C. lindheimerianus: Sepals distinct to base and widest at the apices; abaxial sides of leaves not appearing brown-dotted; low annuals often branching at the base and without a strong main stem (i.e., plants not robust, usually without a primary axis at maturity and widely branching).
C. texensis: Leaves narrow; tall annuals usually with long internodes, not typically branching at the base; sepals less than half the length of fruits at maturity; fruits with distinctive tufts of hair giving a warty or spotted appearance; styles divided many times.
C. fruticulosus: Leaves typically ovate, cordate and distinctly green adaxially; tall shrubby plants.
C. capitatus (east and north margins): Sepals longer than fruit, the tips curving outward at maturity; leaves not cordate; wooly annuals typically with a single main stem (i.e., plants robust, usually with a primary axis and not widely branching), not typically branching at the base.
C. alabamensis (rare): Large shrubs.
C. dioicus (west margin): Silvery perennial herbs, sometimes appearing subshrubby; leaves not acute; styles branches more than 6.
C. pottsii (west margin): Silvery-white perennial herbs, never subshrubby; leaves acute
C. heptalon (southeast margin; see discussion): Like C. lindheimeri but with larger basal leaves, white hairs, and shorter ellipsoid seeds (4 mm long instead of 4.5 mm).
C. michauxii? (east margin): Leaves narrow and silvery abaxially; plants covered in yellow-orange glands.

For differences between C. capitatus and C. lindheimeri, see discussion and illustration in the Flora of North America treatment on Croton. Croton lindheimeri was treated has C. capitatus var. lindheimeri by Manual of the Vascular Plants of Texas and many other references. Flora of North America now treats this entity as a distinct species. Croton lindheimeri is by far the more common than C. capitatus in this region. By far the most distinctive characteristic is the differences in the sepals. The presence or absence of yellow hair as mentioned in FNA doesn't seem to hold up when looking at the observations here. The leaf characteristics seem to work well as long as you understand that C. lindheimeri is variable and often overlap in leaf shape with C. capitatus. If you see a plant with cordate leaf bases, it is almost certainly C. lindheimeri. The petiole characteristic is hard to use in most photos as those of plants much shorter than a person are typically taken from above making it difficult or impossible to see lower leaves. There is also a difference in the seeds described in Manual of the Vascular Plants of Texas but none of the photos on iNaturalist have seeds yet. Croton heptalon looks somewhat in-between C. capitatus and C. lindheimeri with the calices and leaf shape of C. lindheimeri (incurved sepal tips and cordate leaves), but the hair like that of C. capitatus (not yellowish). More distinctions can be found above. FNA considers C. heptalon a South Texas species, though observations potentially representing the plant have been found as far north as the DFW area and as far east as at least Big Thicket National Preserve if not close to the state line. BONAP (probably at least partly incorrectly) lists the species as introduced to 9 other states. If the plant occuring in far East Texas and North Central Texas are C. heptalon, it is possible that the species also occurs in Louisiana and Oklahoma. A reevaluation of the geography and corresponding morphology of C. heptalon is probably needed here. Discussion on the known differences between C. heptalon and C. lindheimeri can also be found here.

List of some observations representative of C. capitatus:
List of some observations representative of C. heptalon:

P.S., Yes, there are three taxa named after Lindheimer: Croton lindheimeri, C. lindheimerianus, and C. glandulosa var. lindheimeri. Thank you Croton taxonomists.

Posted on November 02, 2017 22:54 by nathantaylor nathantaylor | 11 comments | Leave a comment

November 16, 2017

Bias in Observation of the Day

If you are interested in plants, you might have noticed how there is an overall lack of observations that are non-animal. I decided to do a few statistics and found out it's me. 89.3% are animals and only 5.0% are plants (the next largest kingdom represented). Contrasting that with the proportion of animal observations on iNaturalist, only 59.4% are animals while 35.6% are of plants. Surprisingly, the percentages of fungi are extremely close (4.3% and 4.7%). All other kingdoms are less than 1% in both Observations of the Day and iNaturalist in general. Also, both aren't all that different in representation. Here are a couple pie charts to show the representation:

This isn't really that big a deal to me, but it is interesting. Also, I think it would be good for the person or people choosing the observations of the day to know. Lastly, I am clearly biased in my opinion of these statistics since I am a botanist but I think that, in order to encourage a more balanced perspective of the observations on iNaturalist, it would be great to have more plants.

One more thing. I just want to point out that, though the number of plant observations in proportion to animal observations is low, there are actually a huge number of plant observations on iNaturalist (over 2.3 million). This is not a plant vs. animal post. It is simply an observation about the Observation of the Day has a bias toward animals and away from plants in comparison to the proportion of organisms in all kingdoms on iNaturalist.

If you are interested in the percentages, here they are:

All observations:
Plants: 35.6%
Animals: 59.4%
Fungi: 4.7%
Bacteria: <0.1%
Protozoa: 0.1%
Kelp, diatoms, and allies: 0.2%
Archaea: <0.1%
Viruses: <0.1%

Observations of the day:
Plants: 5.00%
Animals: 89.3%
Fungi: 4.3%
Bacteria: 0.1%
Protozoa: 0.6%
Kelp, diatoms, and allies: 0.4%
Archaea: <0.1%
Viruses: 0.1%

The observations that have been observations of the day in the past can be found here. The project itself can be found here.

Posted on November 16, 2017 20:15 by nathantaylor nathantaylor | 22 comments | Leave a comment

November 30, 2017

The common yellow-flowered Medicago species of Texas

Several months ago, I went through a lot of the Medicago observations. I learned a lot about how to tell them apart without fruits, but have since forgotten. Because of this, I have decided to write the information down as I relearn it so that when I do forget, I'll be able to relearn more quickly.

M. lupulina: The species with the most observations and the only yellow-flowered species listed here that has more than 10 flowers per inflorescence. The stipules not lacerate. Fruit without prickles.
M. minima: Stipules not lacerate. Fruits with prickles. Hairy on the upper sides of leaves (and often densely so).
M. polymorpha: Stipules regularly lacerate, less deeply lacerate than M. orbicularis; margin usually not undulating making it relatively easy to detirmine the form of the stipule. Fruits prickled. Not hairy on upper sides of leaves.
M. orbicularis: Stipules irregularly and deeply lacerate, the lacera on the margins often undulating making it difficult to determine the form. Fruits not prickled.

Other Medicago species:
M. arabica: Few flowered. Reddish spot in the middle of each leaflet (apparently fading later in the growing season). Shallowly lacerate stipules. Fruits with prickles.
M. falcata: Many flowered. Similar to a yellow version of Alfalfa (M. sativa). Fruits not curled (falcate) at maturity.
M. sativa (Alfalfa): Many purplish flowers. This is probably easier to confuse with some of the native purple-flowered legumes than the other Medicago species found here.
M. x varia: Hybrid between M. sativa and M. falcata.

My understanding of M. falcata is not as good as the others, but it seems like a pretty distinctive species that needs little more than what is provided to ID. Let me know if you think otherwise. It is also much less common than the others if the number of observations is anything to go by.

Posted on November 30, 2017 21:51 by nathantaylor nathantaylor | 8 comments | Leave a comment

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