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Tuesday - April 25, 2006

From: Austin, TX
Region: Southwest
Topic: Plant Identification
Title: Differentiation between Amorpha roemeriana and A. fruticosa
Answered by: Nan Hampton

QUESTION:

How do I differentiate Amorpha roemeriana and A. fruticosa? Thank you.

ANSWER:

The description in the key in Correll & Johnston Manual of the Vascular Plants of Texas, 1970, p. 817, for False indigo (Amorpha fruticosa) says:

"Leaflets 8-18 (-22) mm. wide; calyx glabrous to variously pubescent. Leaves distinctly petiolate, the petioles 10 mm. long or more. Stalk of the leaflet inconspicuously glandular, if at all; calyx indistinctly glandular; flowering racemes 10-15 ( -20) cm. long."

The description for Roemer's indigo (Amorpha roemeriana) [called in Correll & Johnston by its synonym and former name, Amorpha texana] says:

"Leaflets (15- ) 20-30 mm. wide; calyx uniformly pubescent. Leaflets inconspicuously veined beneath; spikes of inflorescence 10-20 cm. long."

We have a botanical glossary to help with terms that may be confusing.

According to Shinners and Mahler's Illustrated Flora of North Central Texas A. fruticosa is widespread throughout Texas. The range as shown in "Atlas of the Vascular Plants of Texas" Vol. 1 (B. L. turner et al., 2003, Botanical Research Institute of Texas) A. roemeriana has a very small range in Central Texas from Mason, Burnet and Travis Counties in the north to Uvalde and Real in the southwest. There is a small overlap to their ranges.

There are more detailed descriptions of both plants in Correll & Johnston, copies of which can be found at the Faulk Central Library in Austin and in the Life Science Library at the University of Texas.

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