Datura

 
In both D. stramonium and D. metel the plants are glabrous, hairy in D. inoxia
The deciding difference between D. metel and D. stramonium is that mature fruit of D. metel is drooping, covered with short blunt tubercles barely exceeding 3 mm; in D. stramonium mature fruit is erect covered with long spines up to 5 mm long.
In addition the following may help. Plants of D. metel are generally taller less branched and erect often reaching 1.5 m and tend to have purplish stem, in D. stramonium plants are shorter, more branched and spreading, stems not purplish.
The leaves of D. stramonium are generally parted, whereas they are not parted in D. metel 

Luckily you can distinguish them from vegetative plants and flowers also.
1. Plants glabrescent; calyx 5-angled; corolla less than 12 cm long; leaves sinnuate-dentate, anthers less than 5 mm long (capsule erect, 4-valved, with stout up to 5 mm long prickles)...D. stramonium
1a. Plants glabrescent or hairy; calyx cylindrical; corolla more than 12 cm long; leaves entire or sinuate but not
dentate, anthers longer than 1 cm (capsule deflexed, irregularly dehiscent)... 2
2. Plants gladular-pubescent, not purple; calyx 8-10 cm long; corolla 15-18 cm long, anthers 10-17 mm long (capsules deflexed, covered with slender prickles, pubescent, irregularly dehiscent)......................D. inoxia
2a. Plants glabrescent, often purple; calyx 4-9 cm long; corolla 14-20 cm long; anthers 10-12 mm long (capsule deflexed, with short broad-based short prickles, irregularly dehiscent)...............D. metel

  

From Floral Database of Tamilnadu :

 

Binomial Habit               Notes References Distribution Common name
Datura cornigera Hook. (syn. of Brugmansia arborea (L.) Steud.) Shrub Western Ghats,  High Altitude, Cultivated, Native of Tropical America Flora of Tamil Nadu, VOL. II, 1987 Nilgiri
Datura ferox L. Herb Plains, Naturalized, Native of China Flora of Tamil Nadu, VOL. II, 1987 Coimbatore, Tirunelveli
Datura innoxia Mill. Herb Plains , Naturalized, Native of Tropical America Flora of Tamil Nadu, VOL. II, 1987 All districts Oomatthai
Datura metel L. Herb/ Under shrub Plains , Native of Tropical America Flora of Tamil Nadu, VOL. II, 1987 All districts Karu Oomatthai, Oomatthai
Datura sanguinea Ruiz & Pavon (syn. of Brugmansia sanguinea (Ruiz & Pav.) D.Don) Shrub Western Ghats,  High Altitude, Cultivated, Native of Tropical America Flora of Tamil Nadu, VOL. II, 1987 Dindigul, Nilgiri
Datura stramonium L. Herb/ Under shrub Western Ghats & Eastern Ghats, Moist Deciduous Forests Flora of Tamil Nadu, VOL. II, 1987 Coimbatore, Namakkal,  Nilgiri, Salem, Tiruvannamalai Seemai Oomatthai


 

Species with description & pictures in Flowers of India as on 1.1.14:

 

Botanical name Synonyms Family Common name
Datura ferox Solanaceae Fierce Thorn Apple
Datura innoxiaSolanaceae Datura
Datura metel 'Blackcurrant Swirl' Solanaceae Datura Blackcurrant Swirl
Datura metel 'Flore Pleno' Solanaceae Datura Double Purple
Datura metelSolanaceaeDatura Triple Yellow
Datura stramoniumSolanaceaeJimsonweed
Datura wrightii Datura meteloides is a synonym of Datura innoxia Mill.Solanaceae Sacred Datura



  • Datura fastuosa L.
  • Datura innoxia Miller
  • Datura stramonium L.
  • Datura suaveolens Humb. & Bonpland ex Willd. (syn. of Brugmansia suaveolens (Humb. & Bonpl. ex Willd.) Bercht. & J. Presl as per GRIN & The Plant List)
     
  • Datura metel L.
  • Datura stramonium L.
  • Datura suaveolens Humb. & Bonpl. ex Willd. (syn. of Brugmansia suaveolens (Humb. & Bonpl. ex Willd.) Bercht. & J. Presl as per GRIN & The Plant List)
  •  
     
    Indigenous Drugs Of India By Chopra R N, I.C. Chopra (2006- Details-
     
    Medicinal Plants in Andhra Pradesh, India By T. Pullaiah (2002- Details-
     
    Datura arborea L. is a synonym of Brugmansia arborea (L.) Steud.,
    Datura sanguinea Ruiz & Pav. is a synonym of Brugmansia sanguinea (Ruiz & Pav.) D.Don &
     
    Brugmansia & Datura : 1 post by 1 author.
    I have updated efi page on Brugmansia & Datura.
    Attempts have been made to incorporate most of the species available in India & nearby areas with details & keys directly or through links.
    Any comments are welcome.