Key to Rubus spp of Texas (Dewberries, blackberries, and brambles)
Thank you for your interest in brambles and referencing this journal post. Due to the growing effort to further complicate Rubus by adding hundreds of complex species to the iNat database instead of taking the condensed species route like Flora of North America, I have ended my participation in ID'ing Rubus observations. The 3 posts I made will remain online for anyone that cares to reference them.
This post is Part 2 of my series on Rubus species in Texas.
Part 1 - Taxonomy of Dewberries, Blackberries, and Brambles in Texas (Rubus spp)
Part 3 - Rubus spp (of Texas) comparison of features
In June, 2019 I tackled the Taxonomy of Dewberries, Blackberries, and Brambles in Texas (Rubus spp) in a journal post. If you are questioning why there are only 6 valid species of Rubus in Texas, you'll want to head there first. If you are looking for a quick way to figure out which species is which, you can start here.
Two things to keep in mind before we start...
1) Approximately 90% of all Rubus species in Texas are Rubus trivialis. All of the others combined make up the remaining 10%.
2) Common names lead people to pick the wrong ID on iNaturalist, and MANY of the existing observations are identified (and agreed upon) incorrectly because of it. Those darn common names!
This post looks at the three most common species in Texas: R. trivialis, R. pensilvanicus, and R. flagellaris.
For a quick species level ID, you need to photograph or note at least the following:
Habit - Low growing/creeping/trailing vs upright over 3 feet
Stems - With or without bristles
Leaflets - # of leaflets and luster (shiny/not shiny)
For a higher confidence species ID, or to key out your observation at Flora of North America you will also need the following:
Leaflets - Shape of the terminal leaflet, underside of leaflets showing the midveins and surfaces, and pedicels (leaflet stems)
Stipules - (Small leaflike appendages typically in pairs at the base of the leaf stalk.) Shape of the stipules
Flowers - Number of flowers per stem, color of petals
The next thing you will want to be aware of is the difference between bristles and prickles.
Bristles - stiff hairs
Prickles - sharp outgrowth from the stem, similar to a thorn
If your stem has both, it is automatically R. trivialis.
Rubus trivialis ("Southern Dewberry")
QUICK ID:
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Low growing, under 1 foot high 
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Stems with prickles and bristles 
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3 or 5 shiny leaflets, somewhat narrow
|
|---|
"Rubus trivialis is distinguished from other species of Rubus by its frequently glandular-bristly and generally creeping stems, abundant recurved prickles, and typically persistent or semipersistent, lustrous primocane leaves with relatively narrow leaflets."
HABIT: Trailing, or erect but low growing; under 1 foot high
STEMS: Armed with prickles and bristles, glabrous (no fine hairs)
PRICKLES: broad-based, recurved (curved backward)
BRISTLES: glandular tipped, absent to sparse to dense
LEAVES: 3-5 leaflets, relatively narrow and lustrous (shiny) on top
FRUIT/FLOWERS: 1-flowered (sometimes up to 3), petals white to pink. (In MY experience, this species fruits first in the season and has larger fruit, but I haven't verified that.)
The full description of R. trivialis can be found at Flora of North America.
Rubus pensilvanicus ("Pennsylvania Blackberry")
QUICK ID:
Grows upright 3-9 feet
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Stems with only prickles
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5 rounded leaflets
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|---|
HABIT: Grows upright 3-9 feet
STEMS: Armed with prickles, glabrous or sparsely to densely hairy
PRICKLES: Erect (straight out) or retrorse (pointing backward/down the stem)
BRISTLES: Absent
LEAVES: 5 rounded leaflets, but can be anywhere from 3-7 leaflets, not lustrous (shiny) on top
FRUIT/FLOWERS: 5-12 flowered
- The full description of R. pensilvanicus can be found at Flora of North America.
Rubus flagellaris ("Common Dewberry")
QUICK ID:
Low growing, under 1 foot high
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Stems with only prickles 
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3-5 rounded leaflets, not shiny
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|---|
HABIT: Creeping, or low-arching and then creeping; under 1 foot high
STEMS: Armed with prickles, glabrous (without hairs) or densely hairy
PRICKLES: broad-based, hooked, sparse to dense
BRISTLES: Absent
LEAVES: 3-5 leaflets, not lustrous (shiny) on top, terminal leaflet is usually on a short pedicel (leaflet stem) and lateral leaflets are sessile (without a stem) but this can also be seen in R. trivialis.
FRUIT/FLOWERS: 1–3 flowered, petals white
*Note - R. flagellaris can be extremely polymorphic (variable characters)
- The full description of R. flagellaris can be found at Flora of North America.
CONDENSED FLORA OF NORTH AMERICA KEY TO (TEXAS) RUBUS SPECIES
Added 3/28/2020
I've found the need to refer back to the FNA key a few times, so I'm including the key with only relevant couplets here. You can see the full N. America Rubus key here.
| | ||||
|---|---|---|---|---|
| 1 + |
Growing up to 1 foot tall (rarely to 2 feet in R. trivialis, but then falling); stems usually creeping, sometimes erect but low growing, or higher only when using other vegetation for support Growing over 1 foot tall; stems erect or arching | 2 3 |
||
| 2 + |
Stems: bristles absent; leaves deciduous, some occasionally semipersistent, not lustrous; inflorescences 1–3(–8)-flowered; petals white. Stems: bristles absent or gland-tipped, red to purple, rarely green, slender; leaves persistent or semipersistent, lustrous; inflorescences 1(–3)-flowered; petals white to pink. | R. flagellaris R. trivialis |
||
| 3 + |
Leaflet abaxial surfaces usually closely, densely white-hairy or gray-hairy Leaflet abaxial surfaces usually glabrous or sparsely to densely hairy or puberulent, (not white-hairy or gray-hairy) |
4 R. pensylvanicus |
||
| 4 + |
Inflorescences thyrsiform, elongate, (projected well beyond subtending leaves), 10–60(–100)-flowered. Inflorescences cymiform to thyrsiform, compact, (not projected well beyond subtending leaves), 3–15(–25)-flowered. |
R. bifrons R. pascuus |
Comentarios
I'm not entirely DONE with learning about the Rubus species, so be aware that I will adjust and update (particularly pictures) in the near future. I am also going to publish a table that shows the more specific details of the characters for these 3 species. Your comments and corrections are greatly appreciated! (Here or by PM.)
@sambiology @suz @sonnia @alisonnorthup @gcwarbler @nathantaylor @connlindajo @itmndeborah @paulines @artemis224 @cgritz @lisa281 @pfau_tarleton @baldeagle @gcwarbler @postoak
Feel free to tag others!
This is so great. :)
I love simplified anything, but especially when it's related to keying out. I so appreciate your many hours of work on this!
This is terrific! Thank you!
I’m glad to hear that this isn’t finished, @kimberlietx! It’s fantastic now and I know it will only get better. My Rubus IDs certainly need to be reviewed. Trying to figure out which of the more than 200 taxons to even consider was more work than I ever had time to do. I know that they aren’t raspberries, but beyond that I might as well have been guessing.
Because I probably was just taking a series of steps that convinced me that my guess was very scientific. 😏
Wow! Thats quite a bit of investigating and work! Thanks for sharing this.
Great to see this Kimberlie! This is one of the food items of Swamp Rabbit so good to learn. Thanks for the great effort!
Great job, Kimberlie! Thanks for your work and for sharing with us.
Great info, thanks!
Ok, Kimberlie! I'm going to remember it like a true woman of the South - we can be both prickly and bristly at the same time - and we don't sweat, just break out in a glowing "dew" - thanks for all of your very descriptive work.
Absolutely wonderful! Thank you so much!
Super, very helpful....& the season is almost here! Thanks @kimberlietx!
Looks great!
Well done, @kimberlietx, thanks for the information!
Kimberlie, this ROCKS! You made it so easy to understand and differentiate the species. Thank you for all your work on this! Can't wait to see your next project!
A big thanks to everyone who has shared this post and referred to it in your Bramble IDs for others. More of you are ID'ing them for others at species level now and the overall quality of IDs has improved in DFW tremendously! THANK YOU THANK YOU!! (Now to tackle the rest of Texas...)
Fantastic post. Thank you!
I've added a dichotomous key to the bottom of this post which includes all Texas species.
Thanks Kimberlie!
Great!
Beautiful - I love it!
Such a big help, thank you!
I note that in step 2 of your key above you have reversed R. trivialis and R. flagellaris compared to what is given in FNA:
32 (31) Stems: bristles absent; leaves deciduous, some occasionally semipersistent, not lustrous; inflorescences 1–3(–8)-flowered; petals white. 10 Rubus flagellaris
Stems: bristles absent or gland-tipped, red to purple, rarely green, slender; leaves persistent or semipersistent, lustrous; inflorescences 1(–3)-flowered; petals white to pink. 34 Rubus trivialis
As I read FNA -- if bristles are absent it could any of the species (R. t., R. f., or R.p)....and if bristles are present then it can only be R. trivialis (but absence of bristles does not rule out R. trivialis).
@sbdplantgal Someone else recently pointed out the reversal in the key, but I haven't had time to fix it. I'll follow up after the CNC when I have to fix it and respond to your comment on bristles.
Key corrected. Still intend to go through it again to update photos and remove confusing details.
I can't even begin to tell you how many time I've referred to this article. Thank you so much for writing it!
This is so helpful. Thanks for posting it.