Field Trip Texas 0204

Field trip to Texas, Febr. 15 to Febr. 24, 2004.

In February I joined three U.S. scientists on their field trip to Southern Texas: Prof.Dave Seigler from the University of Illinois in Urbana,Il., Prof. emeritus John E. Ebinger of the Univ. of Illinois in Charleston and Dr. Rick Phillippe, Illinois Natural History Survey, Champaign, Il.

Their primary goals were ecological studies of different Acacia populations in the Chaparral Wildlife Management Area (CWMA) near Artesia Wells, Southern Texas.

Eight of the thirteen U.S. Acacia species are found on the 15.200 acres of the CWMA South Texas brush country. Four of them were blooming during the study period.

With the help of my new friends, I learned quite a lot about Acacia in general and U.S. Acacia in particular, what I condense in this report. I will not mention all the characteristics of U.S. Acacia, but concentrate on the components that are specific to the species. I will also report some details I observed. To get familiar with the flora of the area, I used a new field guide from the Texas Parks and Wildlife Press (1). Further details on New World Acacia are found in the extensive publications of D.Seigler and J.Ebinger (2-7).

Acacia schaffneri (Huisachillo; A.tortuosa)

Was the furthest ahead in bloom with small densely flowered orange to yellow globose heads. There were still not many leaves. On young growth, I saw tiny paired reddish spines. On older twigs the stipular spines were longer (about 2 cm) and grey. Most plants were low spreading shrubs – up to 2m high. The inflorescence exits from a small secondary branch. 2-8 pair of pinnae per leaf, 11-19 pair of leaflets.The rachis gland sits directly between or below the first pair of pinnae, which is a significant difference to A. farnesiana.
Some black velvety pods from last year had remained on the shrubs. One was 10 cm long, open at the side, but still had 10 seeds in it. The seeds had a beige horseshoe (U-shaped) line (pleurogram) 0,5 cm from the outside rim.

The quick test for cyanide, done with freshly grounded flowers and leaves was strongly positive, with seeds it was negative.

Acacia farnesiana (Huisachillo; A. smalli; A. minuta).

A. farnesiana (4,6) is only found in limited numbers in the CWMA. There is one prominent tree just behind the mechanis shop on the way out from the laboratory area. It is a huge tree, over 5m high and over 6 m wide, green all over with fresh leaves, many globose flower buds, but only a small number of open flowers. The primary shoots had 3-6 pair of pinnae with > 10 pairs of leaflets each. The rachis gland is situated halfway between the twig and the first pair of pinnae. Short stipular straight grey spines.
I could not find any pods from last year – neither on the tree nor under it.

We have also seen A. farnesiana south of Laredo in Zapata county and along Interstate 10 between S.Antonio and Houston.
A. farnesiana is planted in Europe to extract the “cassie-perfume” from the flowers. As the plants in Texas only started to bloom, I could not yet enjoy the perfume.

Acacia rigidula (Blackbrush; Chaparro)

A. rigidula presented open flowers and a lot of leaves in different locations. The white or yellow flowers are clustered in oblong spikelets.The spicate form can already be recognised in the small flower buds. Of all the species mentioned in this report, A. rigidula had the most spines which were straight, up to 3cm long and paired at the nodes. Even on the broader grey stems some paired spines, angle about 75 o, occurred. The twice compounded leaves have 2-5 pairs of heavily ribbed leaflets on 1-2 pairs of pinnae. The clearly visible side veins are significant indicators of the species.

The inside of the valves of the pods show a 2mm wide brown pericarpic strip, that is typical for A. rigidula and A. constricata (5). The seeds are comparatively small.
South of Laredo we also found young small brown pods on A. rigidula.

In the Chaparral many of the species were covered with all kinds of lichens. David and Rick collected lichen samples, which they will study further. I took a lot of random fotos.
Some of the A. rigidula trees with the lichens on them were also producing new green leaves.

All the other species found in the CWMA have prickles, no spines. For this report the definition is:
Thorns are a more general term. In Texas there are a lot of thorny plants. They often have twigs with sharp pointed ends like in Prosopis glandulosa (Honey mesquite), Condalia or Ziziphus obtusifolia.
Spines in acacia are stipular and straight – mostly paired. Prickles are part of the epidermis and are short and recurved at the end. They can occur paired, but are mostly single and scattered all over the twigs. These prickles are like catclaws, hence the common acacia names.

Acacia berlandieri (Guajillo; Thornless catclaw)

A. berlandieri is a small to medium sized shrub with multiple basal stems ( diameter to 8 cm) flaring outward to form a rounded crown. A. berlandieri has only primary branches. In the CWMA the new leaves were still small, therefore the stems could all be seen and the bush seemed to be quite “open”. On some specimens the flowerballs were well open, some even already gone. No involucel visible. The leaves have 6-9 pinnae pairs with over 30 leaflet pairs. On the underside of the leaf rachis were small prickles. The flat oval rachis gland was near the node, another one between the last and also between the penultimate pinnae pair.

On and under the trees I found big grey open pods, one 10 cm long and 2,5 cm wide with a small tip at the apex. It probably had formerly carried eight seeds.

The small prickles are curved downwards. At a specimen in the San Antonio Botanical Garden I saw some ligh brownish exudate (resin).

When fully open, the leaves look fernlike and cover all the bush. On our trip South of Laredo we found the bushes much more developed. Near Falcon Dam A. berlandieri had lots of leaves and fresh, flat green pods.

Acacia greggii (Catclaw Acacia)

A. greggii can be found at one of the study areas in the CWMA. Many branches probably coming from the same central base form a small bush, max height 1,5 m. Twigs bear scattered small prickles. There were no leaves ( 1-3 pair of pinnae; 3-7 pairs of leaflets; on the back of the leaflet one can normally only see the main vein), no flowers and no old pods.

Acacia emoryana

A. emoryana is a hybrid between A. berlandieri and A. greggii. In the Chaparral we did not find flowers, leaves or pods. There were practically no prickles. On Harris Ranch, however, the A. emoryana grows 2m high and 3 m wide with many quite straight upright branches. Leaves had 2-4 pair of pinnae, >13 pairs of leaflets and short whitish only slightly recurved prickles. The prickles are mostly scattered. Some are nearly paired. The hybrid flowers are slightly spicate, a mixture between the globular flowers of A. berlandieri and the spicate flowers of A. greggii.

Acacia wrightii (Texas Catclaw)

We found many 4-5m high trees on Harris Ranch near Uvalde, Texas. There were only very few prickles. On young twigs they may be paired, but some fall off later. 2-3 pair of pinnae, 2-3 pairs of leaflets per pinna. No flowers, no pods.
There was also a specimen of A. wrightii in Uvalde behind the McDonalds.


There is a hybrid between A. berlandieri and A. wrightii on Harris Ranch – not far from the group of A. wrightii trees. In this neighbourhood there are no A. greggii.
This hybrid shows some small, slightly recurved prickles only on young branches. They always emerged from a whitish line running vertical on the twig.

There seem to occur various hybrids between A. greggii and A. wrightii, which, however are difficult to differentiate in the field.

Acacia roemeriana

In study area 5 in the CWMA live A. roemeriana can be found. GPS readings: altitude 166m; N 28.32722 o; W 099.41385 o.
It is a small bush with reddish flower buds on a 1 cm long peduncle. Small prickles are sometimes paired at the nodes.
On Interstate 10 direction to Houston at a rest area shortly before exit 591 we also saw A. roemeriana with the reddish flower buds near the twig. No peduncle visible, no leaves, no fruit, some paired prickles!

Acacia angustissima

A. angustissima is a small shrub, which grows further East and North than the other species. There were no leaves, no flowers no pods from last year: On my own I would never have found it behind the mechanics shop in the CWMA.
It is also said to occur in the Houston Botanical Garden. As it was not marked, I did not find it there either.

Acacia neovernicosa

On our trip to West of the Pecos Texas we visited the former home of the legendary Judge Roy Bean in Langtry. There is a small botanical garden, where A. neovernicosa grows, a 1 m high bush. Later in spring, A. neovernicosa (5) has a sticky exudate on the outside of the leaves and is therefore also called sticky leaf acacia or varnished acacia.
There is only one pair of pinnae. Small white paired stipular spines. There were no flowers (dense globose head) or pods. Peduncle glabrous 14-18 mm long with a whorl of involucral bracts near the middle, which is a characteristic feature.

Other U.S. Acacia: A. constricta; A. schottii; A. millefolia; A. auricoliformis


(1) A Field Guide to Common South Texas Shrubs
ISBN 1-885-696-14-0
R.B.Taylor, J.Rutledge, J.G.Herrera

(2) A systematic treatment of Acacia Coultieri (Fabaceae, Mimosoideae) and similar species in the new World
J.T.Jawad, D.S.Seigler, J.E.Ebeinger
Ann. Missouri Bot. Gard. 87: 528-548. 2000

(3) Taxonomic revision of South American Species of the genus Acacia, subgenus Acacia (Fabaceae: Mimosoideae)
J.E.Ebinger, D.S.Seigler, H.D.Clarke
Systematic Botany (2000), 25(4): pp 588-617

(4) Acacia farnesiana (Fabaceae: Mimosoideae) and related species from Mexico, the Southwestern U.S., and the Caribbean
H.D.Clarke, D.S.Seigler, J.E.Ebinger
Systematic Botany 1989 (14) pp549-564

(5) Acacia constricta (Fabaceae: Mimosoideae) and related species from the Southwestern U.S. and Mexico
H.D.Clarke, D.S.Seigler, J.E.Ebinger
Amer. J. Bot. 77 (3) pp305-315. 1990

(6) Notes on the segregates of Acacia farnesiana (L.) WILLD. (Fabaceae: Mimosoideae) and related species in North America
J.E.Ebinger, D.S.Seigler, H.D.Clarke
The Southwestern Naturalist 47 (1) pp 86-91. 2002

(7) Evaluation of toxicity of Acacia angustissima in a rat bioassay
A.H.Smith, A.A. Odenyo, P.O. Osuji, M.A. Wallig, F.E. Kandil, D.S. Seigler, R.I. Mackie
Animal Feed Science and Technology 91 (2201) pp 41-57