Rosa acicularis
 
Prickly Rose

Flower in Ground

Whirlpool Lake in Riding Mountain National Park
22-June-2010

Rosa acicularis and Rosa woodsii are sometimes difficult to distinguish, and in addition they occasionally hybridize.  The following table contains characteristics for each of these species taken from a number of flora (listed at the bottom of the table).   The entry for the first row, taken from Plants of the Western Boreal Forest & Aspen Parkland (PWB), is probably the most reliable way to distinguish between the species.  Note that the difference applies just to the upper or current year's stems.  Lower stems of both species are well armed.      

Rosa acicularis Rosa woodsii
Upper stems usually densely covered with many straight, weak bristles and straight, slender thorns (PWB) Upper stems lack many small bristles and prickles, instead have a few scattered thorns, usually at stem nodes (PWB)
Stems bristly to tips (FOA1) Stems with scattered bristles or bristly at base only (FOA1)

Stem and branches very bristly (FOC)

Stem less bristly, the bristles scarcely (if at all) extending into the branches (FOC)

Stem-prickles uniformly dense throughout (FOA2)  

Stems and branches densely covered with bristles and with straight terete prickles (FYT)

Stems less densely armed and branches often bearing only infrastipular prickles (FYT)

Thorns not present (BF)

Thorns present below the stipules (BF)

Thorns directly below the stipules none or not different from the internodal ones (FOA1)

Thorns commonly present at the base of the stipules (FOA1)

Infrastipular prickles absent (FOA2) Infrastipular prickles present, conspicuously larger and stouter than the stem-prickles (FOA2)

Stems without infrastipular prickles or these not differentiated from those of the internodes. (FGP)

Stems usually with well-defined infrastipular prickles.  (FGP)

Infrastipular prickles not clearly differentiated from those of the internodes (FOC)

 

Bristles usually not broad or flattened at the base (BF)

Bristles broad and usually flattened at the base (BF)

Stipules densely glandular (FOA2) Stipules sparsely glandular (FOA2)

The leaf-rachis usually glandular (FOC)

 

Leaflets commonly 5-7 (FOA1)

Leaflets usually 5-9 (FOA1)

Leaflets 3-7, commonly 5, rarely 9 (FOA2) Leaflets 5-7 in some plants, 7-9 in others (FOA2)

Leaflets oblong-elliptic, often 3-4 cm long, irregularly dentate-serrate, the teeth acute (FOA1)

Leaflets oval to obovate, mostly 1-3 cm long, regularly serrate, the teeth often acuminate (FOA1)

Leaflet base obtuse or rounded (FOA2) Leaflet base acute (FOA2)
Leaflets generally more than 25 mm long (FOA2) Leaflets generally less than 25 mm long (FOA2)

Leaflets often resinous-puberulent beneath (FOC)

 

Flowers solitary (rarely 2) on lateral branches of the season (FOC)

Flowers mostly in corymbiform cymes terminating the lateral branches of the season (FOC)

 

Petals to 2.5 cm long (FOC)

Sepals ascending at maturity, beak-like at the summit of the fruit (FOC)

Sepals to about 1.5 cm long, glabrous to puberulent or occasionally inconspicuously glandular (rarely coarsely stipitate-glandular) (FOC)

Fruit oval with distinct neck (BF)

Fruit globose without constricted neck (BF)

Fruit globose (lacking a neck) to pear-shaped, with a distinct neck below (FOA2) Fruit globose, lacking a neck below (FOA2)

Rosehip round to pear-shaped with a distinct stalk or “neck” below (WOP)

Fruits are spherical but lack a neck (WOP)

BF – Budd’s Flora                                     FGP – Flora of the Great Plains 
FOA1 – Flora of Alberta, First Edition     FOA2 -
Flora of Alberta, Second Edition
FOC – Flora of Canada                           
FYT – Flora of the Yukon Territory
PWB - Plants of the Western Boreal Forest & Aspen Parkland
WOP – Weeds of the Prairies

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Acicularis: Answers to key questions in Budd's Flora (BF) and Flora of Alberta (FOA) leading to this species. 
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plant shrubby; NOT [plant partly shrubby, often dying back close to the ground in winter] (BF)

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stems persistent, branched, generally more than 5 dm tall; NOT [stems mostly dying back each year to near ground level] (FOA)

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plant definitely bristly; NOT [plant with few, if any, bristles] (BF)

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infrastipular prickles absent; NOT [infrastipular prickles present, conspicuously larger and stouter than the stem-prickles] (FOA)

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thorns NOT present; NOT [thorns present below the stipules] (BF)

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stem-prickles uniformly dense throughout (FOA)

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stem-prickles to 5 mm long; NOT [stem-prickles to 3 mm long] (FOA)

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bristles usually not broad or flattened at base; NOT [bristles broad and usually flattened at the base] (BF)

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stipules densely glandular; NOT [stipules sparsely glandular] (FOA)

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leaflets usually 5-9 (9 on young shoots); NOT [leaflets 9-11] (BF)

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leaflets 3-7; NOT [leaflets mostly 5-9] (FOA)

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leaflets (3) 5-7 (9); NOT [leaflets (7) 9-11] (FOA)

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leaflets generally more than 25 mm long; NOT [leaflets generally less than 25 mm long] (FOA)

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leaflet base obtuse or rounded; NOT [leaflet base acute] (FOA)

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leaflet lower surface and teeth generally glandular; NOT [leaflet lower surface and teeth not glandular] (FOA)

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in flower mid-June to mid-July; NOT [in flower late June to August] (FOA)

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flowers 1-3, rarely more; NOT [flowers (2) 3-many, born on the generally unbranched stem(s) of the current year which are usually 1-4 dm tall] (FOA)

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flowers usually borne singly (BF)

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fruit globose (lacking a neck) to pear-shaped, with a distinct neck below; NOT [fruit globose, lacking a neck below] (FOA)

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fruit oval with distinct neck (BF)

 

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Rosa: Answers to key questions in Budd's Flora  and Flora of Alberta leading to this genus. 
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shrubs; NOT [small trees], NOT [herbs, or with a woody base and otherwise herbaceous]

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plants generally taller; NOT [plants 5-15 cm tall]

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leaves compound, distinctly divided into leaflets; NOT [leaves simple], NOT [leaves lobed, not distinctly divided]

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leaves NOT linear-dissected; NOT [leaves dissected into linear divisions]

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leaves with 5-11 leaflets; NOT [leaves with 3-5 leaflets], NOT [leaflets 11-17]

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hypanthium shaped like a saucer, cup or urn

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sepal bractlets absent; NOT [bractlets alternating with the sepals]

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flowers white or pink; NOT [flowers yellow]

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carpels numerous; NOT [carpels mostly 5], NOT [carpel 1]

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ovary or ovaries superior; NOT [ovary inferior]

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ovary free from hypanthium; NOT [ovary enclosed in and adnate to the hypanthium]

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fruit more or less fleshy; NOT [fruit dry]

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carpels becoming achenes, enclosed in a fleshy receptacle; NOT [carpels becoming drupelets (raspberry-like)]

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fruit a bottle-shaped “hip”; NOT [fruit a cluster of many fleshy drupelets]

 

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Rosaceae: Answers to key questions in Budd's Flora  leading to this family. Not all the answers apply to all members of Rosaceae found on the Canadian prairies, but they all do apply to this species.
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shrubs or trees; NOT [herbs]

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plants NOT climbing

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plants with normal leaves

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leaves alternate; NOT [leaves opposite]

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leaves compound; NOT [leaves simple]

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leaflets NOT leathery

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leaflets NOT spinose-tipped

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flowers with two floral rings, and with each petal distinct from the others

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flowers perfect; NOT [flowers dioecious or perfect]

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petals 5; NOT [petal (standard) solitary]

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stamens numerous; NOT [stamens 5]

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fruit NOT a legume