Rubus spp (of Texas) comparison of features



This post is Part 3 of my series on Rubus species in Texas.

Part 1 - Taxonomy of Dewberries, Blackberries, and Brambles in Texas (Rubus spp)
Part 2 - Key to Rubus spp of Texas (Dewberries, blackberries, and brambles)



In Part 2 I presented a guide to Quick ID the three most common Rubus species in Texas. This post takes species identification to the next level. It is an extract and comparison of the detailed characteristics of each species from the Flora of North America website. There is much value in looking closer at the leaflet shape and size, for example, in helping to determine species for observations that are inconclusive from the Quick ID guide. The botany terminology is heavy, so if you have a dictionary handy you will want to get it.
 R. trivialis R. pensilvanicus R. flagellaris
HABIT Shrubs to 3(–7) dm, moderately to densely armed Shrubs 10–30 dm, armed Shrubs to 3 dm, armed
STEMS biennial biennial biennial
initially low-arching, then falling and creeping (or climbing higher through other vegetation) erect to arching usually creeping, sometimes low-arching and then creeping , flowering branches usually erect
glabrous or moderately hairy glabrous or sparsely to densely hairy glabrous or densely hairy
sparsely to densely short- to long-stipitate-glandular eglandular or sparsely to moderately, rarely densely, sessile- to short-stipitate-glandular eglandular or sparsely sessile- to short-stipitate-glandular
not pruinose not pruinose not pruinose
PRICKLES moderate to dense prickles sparse to dense prickles sparse to dense
recurved erect or slightly retrorse hooked
sometimes distally slender, 1–4 mm, broad-based stout, 4–10 mm, broad-based sometimes distally slender, 1–4 mm, broad-based
BRISTLES absent or sparse to dense absent
erect to retrorse
red to purple, rarely green
slender, weak
gland-tipped
LEAVES persistent or semipersistent deciduous deciduous, some sometimes semipersistent
ternate to palmately compound palmately compound ternate or palmately compound
lustrous not lustrous not lustrous
Stipules stipules filiform, linear, or lanceolate; 2–12(–15) mm filiform to narrowly lanceolate;  (3–)5–15(–20) mm stipules filiform or linear to lanceolate, 3–20 mm
Leaflets leaflets 3–5 leaflets (3–)5(–7) leaflets 3–5
Terminal shape terminal narrowly elliptic or ovate to obovate terminal ovate to lanceolate terminal ovate or elliptic to suborbiculate
Size 5–15 × 3–13 cm 3–11 × 2–7.5 cm
Base base rounded to cuneate base rounded to shallowly cordate base broadly cuneate or rounded to shallowly cordate
Lobes unlobed unlobed usually unlobed, rarely shallowly lobed
Margins margins moderately to coarsely serrate to doubly serrate margins finely to coarsely singly or doubly serrate margins moderately to coarsely serrate to doubly serrate or serrate-dentate
Apex apex acute to acuminate apex acuminate to long-attenuate apex acute or acuminate to short-attenuate
Abaxial surface abaxial surfaces with hooked prickles on midvein abaxial surfaces green, usually with retrorse prickles on midvein abaxial surfaces with prickles on midvein or unarmed
glabrous or sparsely to moderately hairy moderately hairy sparsely to moderately hairy
eglandular or sparsely short-stipitate-glandular along central vein eglandular or sparsely to moderately sessile- to short-stipitate-glandular along veins eglandular or sessile- or short-stipitate-glandular along largest veins.
INFLORESCENCES terminal, on short shoots usually appearing axillary terminal, on short shoots usually appearing axillary terminal, on short shoots usually appearing axillary
1(–3)-flowered (2–)5–12(–16)-flowered 1–3(–8)-flowered
cymiform, racemiform, or thyrsiform racemiform
Flowering Jan–Jun Flowering May–Jul Flowering Mar–Jun
PEDICELS prickles and, often, bristles moderate to dense, recurved unarmed or prickles sparse, erect unarmed or prickles sparse to moderate, retrorse to hooked
moderately to densely hairy glabrous or sparsely to densely hairy moderately to densely hairy
sparsely to moderately sessile- to short-stipitate-glandular eglandular or sparsely to moderately sessile- to short-stipitate-glandular usually sparsely to densely sessile- or short-stipitate-glandular, rarely eglandular
FLOWERS bisexual bisexual bisexual
petals white to pink petals white petals white
elliptic to obovate, 10–16(–25) mm usually obovate to elliptic, rarely suborbiculate, 8–40 mm elliptic, obovate, or oblanceolate, 8–20 mm
filaments filiform filaments filiform filaments filiform
ovaries glabrous ovaries glabrous ovaries glabrous
FRUITS black black black, sometimes dark red
globose to ovoid, 1–1.5(–2) cm globose to cylindric, 1–2 cm globose to cylindric, 1–2 cm
drupelets 10–50 drupelets 10–100 drupelets 10–40
strongly coherent, separating with torus attached strongly coherent, separating with torus attached strongly coherent, separating with torus attached
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. Although emerging primocanes typically reach to 30 cm above the ground, vigorous plants can have new primocanes standing erect to 70 cm that later fall to the ground or onto adjacent vegetation as they continue to enlarge.

Rubus flagellaris is extremely polymorphic, ranging from plants with low-arching (and later creeping) stems and relatively few prickles to low, creeping plants with abundant prickles. Individual plants in some years will produce abundant, arching, poorly armed stems, and in others creeping, well-armed stems. Prickle shape also varies in these plants both within a year and among different years. Local variants seem to readily intergrade with other variants.

Apparent consistent features of Rubus flagellaris are terete primocanes to 7 mm diam. near the base and presence of rigid, hooked primocane prickles to 4 mm. Primocanes that tip-root and are low and long-running are nearly consistent features of R. flagellaris. Flower number per inflorescence throughout most of the geographic range of R. flagellaris is one to three or, rarely, five.

Posted by kimberlietx kimberlietx, February 01, 2020 23:18

Comments

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I can only imagine how much time you've spent on this study. Thank you!

Posted by suz 8 months ago (Flag)
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@suz A lot of hours! With more to go to photograph the details this season, test out the key using in situ plants, and a tackle some random questions I have left over. It's been fun though! I wanted to get it posted before Anemone season gets here. :)

Posted by kimberlietx 8 months ago (Flag)
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Cool, congrats!

Posted by gernotkunz 8 months ago (Flag)
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From a neighbor in Louisiana, Thank You!

Posted by t-j-w 6 months ago (Flag)
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I see some berries are tight and compact with small drupelets and some have big, round drupelets that are more likely to split apart from each other. I have one plant that makes berries with both large and small drupelets at the same time (same berry). Is this species variation, hybridization, or just a variable factor within a species (I think all R. trivialis).

Posted by arborworks 5 months ago (Flag)
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@arborworks I would guess that variation on the same plant would be related to weather (warmer/cooler temps, rainfall, etc.) The table above shows detailed info about the drupes for each species. I'd recommend confirming the species, which is easy for R. trivialis since you can just look at the stem for prickles and bristles. More info here: https://www.inaturalist.org/journal/kimberlietx/30266-key-to-rubus-spp-of-texas-dewberries-blackberries-and-brambles

Posted by kimberlietx 5 months ago (Flag)
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thanks!

Posted by arborworks 5 months ago (Flag)

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