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Annual or perennial herbs or shrubs, rarely trees, sometimes root parasites. Leaves usually opposite, occasionally verticillate, rarely alternate, simple or sometimes pinnately dissected. Flowers solitary or in axillary or terminal spikes, racemes or cymes, usually zygomorphic, rarely actinomorphic. Calyx tubular or campanulate, 4- or 5-lobed. Corolla sympetalous, limb often 2-lipped, lobes 4 to 5. Stamens mostly 4, didynamous, sometimes 1 or 2 staminodes present. Ovary superior, 2-loculed, styles simple, terminal, stigmas capitate, 2-lobed or 2-lamellate. Fruit a capsule, septicidal, loculicidal or septifragal, rarely a berry, usually 2-valved, less often 3-4 valved. Seeds minute or rarely conspicuous, sometimes winged.

Key to the Genus

Serial Key Reference
1a. Corolla tube bulging or spurred at base in front; limb personate, the palate in the lower lip enclosing the throat; upper lip also 2-gibbous; capsule opening by pore 2
1b. Corolla tube not enlarged at base in front; limb not personate; capsule dehiscing by valves 4
2a. Corolla spurred in front at the base Kickxia
2b. Corolla saccate in front at the base, often 2-tuberculate at base 3
3a. Corolla throat broadened into a sac like cup, often 2-tuberculate at base, lobes spreading Angelonia
3b. Corolla throat with bearded broad palate closing the throat Antirrhinum
4a. Corolla with upper lip or two upper lobes outermost and lower lobe innermost in the bud 5
4b. Corolla with upper lip or two upper lobes innermost in bud or imbricate. Upper lip of corolla rounded, corolla throat densely long-hairy, stamens 4 Scoparia
5a. Corolla nearly actinomorphic; tube short. Fertile stamens 5 or 4 in few flowers Verbascum
5b. Corolla zygomorphic or bilabiate; tube at least as long as lobes. Fertle stamens 2 or 4 6
6a. Corolla elongated; tube cylindric with more or less expanded throat; limb distinctly 2-lipped, or, if lobes unequal, with 4 stamens 7
6b. Corolla small, tube very short, uniform; lobes subequal; stamens 2, filaments filiform 18
7a. Stamens if 4 all, if 2 (Dopatrium) both staminodes and filaments inserted within the tube 8
7b. Stamens if 4, the anterior pair, if 2, the staminodes attached to corolla throat, the posterior or only perfect pair inserted within corolla tube 16
8a. Corolla not distinctly 2-labiate; lobes all rounded; anther cells divaricate, confluent 1-locular; capsule septicidal. Leaves opposite or whorled, capsule subglobose Russelia
8b. Corolla distinctly 2-labiate, or if lobes subequal (Bacopa) the anther cells contiguous but distinct; capsule loculicidal or both loculicidal and septicidal 9
9a. Corolla throat 2-gibbous; anther cells divaricate 10
9b. Corolla throats not 2-gibbous; anther cells distinct 11
10a. Calyx 5-angled and 5-toothed; anther cells confluent, often 1-celled; leaves all opposite Mimulus
10b. Calyx wide-campanulate, 2-fid; anther cells contiguous but distinct; lower leaves opposite, upper alternate Mazus
11a. Stamens 4; corolla throat little widened 12
11b. Stamens 2, perfect, the anterior pair reduced to staminodes; corolla throat much widened. Calyx deeply 5-fid Dopatrium
12a. Calyx wide campanulate, 2-fid; corolla throat with 2-parallel ridges; anther cells disjoined, stipitate; capsule loculicidal Lindenbergia
12b. Calyx 5-patrite; corolla throat without ridges; capsule both loculicidl or septicidal 13
13a. Anther cells contiguous though distinct. Calyx 5-patrite, lateral segments in most much narrower than others; corolla with 5 subequal lobes 14
13b. Anther cells disjoined, stipitate 15
14a. Outermost sepals not cordate; anther locules parallel; stigma dilated, capitate; capsule loculicidal or 4-valved Bacopa
14b. Outermost sepals cordate; anther locules divaricate; stigma 2-lamellate; capsule septicidal Picria
15a. Upper most lobe of calyx considerably or much exceeding the others; 2 or all stamens with one perfect cell Adenosma
15b. Upper most lobe of calyx not much, if at all, larger than the others; all the stamens perfect. Placentas always conjoined in a column, winged by remains of septa, seeds angular Limnophila
16a. Calyx 5-patrite; 5-ridged or winged 17
16b. Calyx 4-patrite, without wings. Upper and lower calyx lobes large, the lateral lobe narrow, perfect stamens 2 Curanga
17a. Ovary ovate, oblong or cylindric, glabrous all over. Calyx deeply to shallowly lobed, generally ridged, rarely with narrow wing. Anterior stamens fertile, sterile or reduced to filiform staminodes Lindernia
17b. Ovary obliquely cylindric, with short scabrid hairs at upper part. Sepals united over half of calyx length, winged or ridged Torenia
18a. Calyx campanulate, with 3-4 short, obtuse lobes; leaves opposite or fascicled Glossostigma
18b. Calyx tubular; leaves opposite 19
19a. Calyx lobes unequal, outermost largest; stamens 4 Mecardonia
19b. Calyx 5-angled or ribbed; stamens 2 Microcarpaea