Tribulus

 

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Tribulus complex : Attachments (1). 3 posts by 3 authors.

This image from my ppt slide has pictures of 3 species of Tribulus. They are distinct in general morphology, style, fruits, thorns, indumentum, leaves etc. as you can see in the pictures.
Reproducing the key here: 
A simple macroscopic key to distinguish the 3 southern indian species :
1. Style absent or very short (< 0.5 mm long) — Tribulus terrestris
1. Style present, 1.5-2 mm long —- 2
2. Style glabrous —- Tribulus lanuginosus (syn. of Tribulus terrestris var. bicornutus (Fisch. & C. A. Mey.) Hadidi)
2. Style pubescent —— Tribulus subramanyamii 
Hope this gives some clarity in id of these 3 spp.
Look forward to your comments/observations.

Really useful information sir. Thank you very much for sharing and throwing light on this species complex.

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Taxonomic Status of Some of the Tribulus Species in the Indian Subcontinent by Varghese, M.; Yadav, S.S. & Thomas, J.  Saudi Journal of Biological Sciences 13 (1) 7-12: 2006 (keys)–
A provisional key for the determination of  Tribulus L. in India
1. Mericarps winged   2
1+ Mericarps spiny or unarmed or look-like unarmed   3
2. Stamens usually 5; wings of mericarps 2-4 mm wide or represented by small spinules at the base of the mericarps; margin of the wing much dentate … T. pentandrus
2+ Stamens 8-10; wings of mericarps 6-10 mm wide; margin shortly or shallowly few dentate. … T. macropterus
3. Flowers smaller, 5-15 mm wide    4
3+ Flowers larger, 25-40 mm wide. … T. cistoides
4. Mericarps with two lateral spines and 20-25 unequal spines spreading throughout … T. terrestris var. rajasthanensis
4+ Mericarps with 2 lateral spines and two basal spines or the basal spines absent.   5
5. Style puberulous, intra staminal glands connate and ciliated. … T. subramanyamii
5+ Style glabrous, intra staminal glands free, not cilated   6
6. Flowers 5-7 mm wide; Stamens 5-8; fruit 6-8 mm in diameter including spines; lateral spines 1.5-3 mm long; basal spines small or reduced to tubercles. … T. parvispinus
6+ Flowers 7-15 mm wide; Stamens usually 10; fruit 9-15 mm in diameter including spines; lateral spines5-8 mm long; basal spines 3-5 mm long. … T. terrestris

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Taxonomic Status of Some of the Tribulus Species in the Indian Subcontinent by Varghese, M.; Yadav, S.S. & Thomas, J.  Saudi Journal of Biological Sciences 13 (1) 7-12: 2006 (Details with keys–

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BSI Flora of India with keys (Volume 4) (Distribution):
Tribulus cistoides L. (No one has reported its occurrence in wild in India)
Tribulus lanuginosus L. (India: In most of the states)
Tribulus pentandrus Forssk.
var. macropterus (India: Common in sandy habitats. Rajasthan; Pakistan, Afghanistan to N. Africa)
var. pentandrus (India: usually on sandy habitats; Punjab, Haryana and Rajasthan; Pakistan, Afghanistan, Iran, Iraq, Israel, Arabia, Somalia, Sudan and N. Africa)
  var. pterophorus (India: Rajasthan; Pakistan, Afghanistan and S.W. Africa)
Tribulus rajasthanensis Bhandari & Sharma (India: Rajasthan and Gujarat; Pakistan)
Tribulus subramanyamii P. Singh, Giri & V. Singh (India: Common weed of wastelands. Maharashtra, Andhra Pradesh, Karntaka and Tamil Nadu; Endemic)
Tribulus terrestris L. (India: Common weed of waste places, road-sides and fallow lands of sandy and gravelly habitats; throughout from sea level to 3500 m. Pantropical)

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Flora of Peninsular India with keys at book links:
Tribulus lanuginosus var. orientalis
Tribulus rajasthanensis
Tribulus subramanyamii
Tribulus terrestris

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Species with description & keys from Flora of Pakistan (Distribution):
Tribulus longipetalus Viv.
  Tribulus longipetalus subsp. longipetalus (Afghanistan, S.W. Asia, Arabia, Sudan, Somalia and North Africa)
  Tribulus longipetalus subsp. macropterus (Boiss.) Maire ex Ozenda & Quezel (Pakistan westwards to North Africa)
  Tribulus longipetalus subsp. pterophorus (Presl) Hadidi in Rech. f. (South West Africa, Caput Bonei Spei, Afghanistan and Pakistan (Baluchistan))
 Tribulus ochroleucus (Maire) Ozenda & Quezel (Pakistan, Afghanistan, Iran, North Africa, Chad, Niger and Somalia)
Tribulus pentandrus Forsk. (India, Pakistan, Iran, Iraq, S.W. Arabia, tropical and North Africa, Madagascar and South Africa)
Tribulus terrestris Linn. (Tropical and subtropical countries in Asia, Africa, S. Europe, North Australia and introduced in new world tropics)

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Species with distribution in annotated checklist of Flowering plants of Nepal (Distribution):
Tribulus terrestris L. (150 m; Almost Pantropical)

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Species with description & keys in Flora of China (Distribution other than China):
Tribulus cistoides Linnaeus [throughout tropics]
Tribulus terrestris Linnaeus [almost worldwide]